Electronic component suppliers

Method
Buy first from Tayda, then if they don't have the part from Mouser and then from Digikey. For synth specific components buy from Thonk, synthCube or Modular Addict. Parts will be cheaper per component if you buy in larger quantities. Do this often enough and you'll get to know which parts you use the most of. If you must buy components off Amazon, buying direct from branded sellers is safer. Specialist or difficult to obtain parts from Amazon resellers are often counterfeit, passive devices, or common general purpose diodes or transistors are less risky.

First check AliExpress (see below) or Chinese suppliers on eBay for cheaper equivalent parts, but with taking longer for delivery.

In addition, you will have to pay for shipping, taxes and depending on your location import duty.

Listed by country
Unless stated otherwise these all ship internationally. For general electronic supplies including hardware, by mail order.

China

 * Alibaba.com
 * Also via eBay
 * LCSC
 * Sure Electronics
 * UT Source A supplier of hard to find semiconductors. Usually okay, but has had some noted occurrences of counterfeit parts being supplied (though they normally replace or refund for the affected parts).

AliExpress
On AliExpress select items with highest number sold and the highest rating. The same sellers might be on eBay with better shipping options. Buy enough to make up for the odd fake or broken part if any. Test less common active component types (diodes, transistors, ICs, and so on) before use.

Czech Republic

 * dsm components - new and surplus electronic components. Reasonably priced shipping.

Finland

 * Ural Tone Mainly a supplier of Valve Amplifier and Guitar parts, but a good range of Reverb tanks and some components.

Germany

 * Ask Jan First - tube and antique electronics
 * Banzai Music - supplies various hard to find components, but mainly focused on guitar effects.
 * Darisus - a wide range of electronic components, including some rare semiconductors. Ships internationally.
 * Das Musikding - a similar supplier to Banzai, with a good range of parts.
 * Led-tech - LEDs
 * Munichen Audio Synth and Audio DIY
 * Reichelt Elektronik - Reichelt used to be European only, but now ships internationally. Supplies quite a few of the unusual parts used in Jürgen Haible's designs.

Switzerland

 * Ghielmetti Maker of matrix patchboards

The Netherlands

 * Synfo / Vintage Planet – One man shop (Senso) for synth repairs & rare parts. Ships international. This site has now closed, with Senso now selling these parts via eBay.

Portugal

 * Electricdruid/ Synth chip supplyer

UK

 * Action Hardware – distributor of Switchcraft connectors, often with better prices than other UK based suppliers.
 * AliExpress -
 * Arrow Electronics
 * Bitsbox - "Small selection but very cheap. " Delivery for £1.75 regardless of order size.
 * Ciseco - microcontrollers, radio modules, Raspberry Pi expanders.
 * CLIFF Electronic Components Ltd. - jacks and knobs used on many synths.
 * Cool Components - Sparkfun stuff.
 * CPC - is actually owned by Farnell, but are sometimes cheaper than Farnell for the same items. Free delivery on orders over £5. Consumer-oriented.
 * Cricklewood Electronics - general supplier of components, has some hard to find semiconductors.
 * Digikey - USA based but free shipping for orders over £33. Like Mouser but bigger range and typically a little more expensive.
 * Earthshine Electronics - Arduinos and other parts.
 * eBay -
 * Electron Electronics - orders over £30 are shipped free.
 * ESR - general supplier of components. Half the price of farnell for some parts.
 * Farnell - has almost everything. Trade-oriented. Owns CPC and Newark. CPC are sometimes cheaper than Farnell for the same items. Free shipping if above minimum order.
 * Future Electronics
 * Futurlec - Based in Thailand, very cheap, very slow to deliver and very poor reputation. Have SMD to DIP converter's which are useful for prototyping.
 * Goodwill - LEDs
 * Greenweld - general supplier of components, has some hard to find semiconductors.
 * Hobby Tronics - general supplier of components and Sparkfun stuff. Delivery costs £2.40 for orders under £50.
 * Infinite Machinery, integrated cicuits and components for the DIY audio community.
 * JPR Electronics - Minimum order £30.00.
 * Led-tech - LEDs
 * LinkSprite - open source electronics, pcDuino, communication modems.


 * Mallinson Electrical - aims to offer good quality and low prices for small quantities.
 * Mega Electronics PCB-making supplies. Their products are also sold by Farnell and Rapid but may be cheaper direct.
 * MMS Electronics - SPI/I2C graphic LCDs.
 * Model Fixings - a useful supplier of small nuts and bolts.
 * Mouser USA based but free shipping for orders over £33. Farnell is cheaper.
 * Nikko Electronics - massive range, many rare/hard-to-find parts. Good reputation. Ships international.
 * Northern Connectors - specialist connector distributors. Mainly bulk deals but order threshold is low.
 * Online Components - has a large catalog of electronic components.
 * Oomlout - Arduino & DIY electronics.
 * Proto-pic - Adafruit, Sparkfun, BBC Micro:Bit, Pololu, Raspberry PI and various electronics.
 * Rapid - usually cheaper than RS or Farnell for run-of-the-mill parts. Website awkward to navigate. Sister company to RS with a smaller range but sometimes cheaper. Free delivery on orders over £30. "Typically the cheapest. "
 * R F Potts - an independent electrical and electronic components spares shop in Derby.
 * RS - has most things, trade-oriented, usually more expensive (especially for small orders).
 * Seeed studio -
 * Sparkfun electronics -
 * Spiratronics - "Small selection but relatively cheap. "
 * Tayda Electronics - Thailand based, hobbyist supplier. Orders must be over $5. Low cost and reasonable quality. Shipping is cheap and might take a week or two to arrive. Good customer service by email. Regularly discount codes posted on their Facebook page.
 * Thonk - parts especially for synth DIY
 * TME.eu - electronic components, very competitive value.
 * Toby UK - specialising in board-board and signal-board connectors. Potential UK supplier of hard-to-find extra long pin headers as used by the Arduino platform.
 * Wires.co.uk - unusual wire, enamelled, knitted, litz etc.

Obsolete, surplus and new old stock

 * Antique Electronic Supply
 * Arcadecomponents.com
 * Bull Group Ltd. - Surplus dealers. Used to be Bull Electrical. Difficult to find anything interesting on the website.
 * Cyclops
 * Electrojumble
 * Express Online
 * Keytronics
 * Langrex - "one of the largest stocks of obsolete and hard to find commercial, industrial and military components in Europe".
 * mark5 - obsolete and hard-to-find electronic components.
 * RSGB rallies
 * Silicon-Ark
 * Sinequanon
 * Surplectronics - surplus electronic components and semiconductors

USA
See also Info on how to get electronic parts at AdaWiki and Component and Parts Suppliers at r/AskElectronics wiki Excelitas) Vactrols right now.
 * synthCube
 * Modular Addict
 * 4 Site Electronics – Good parts supplier. Specializes in effect-pedal parts, also has an excellent selection of analog joysticks.
 * Allied – Large industrial distributor, not hobbyist-oriented. Prices tend to be much higher than other firms. Best supplier of Perkin-Elmer (now called
 * All Electronics
 * Amplified Parts - Synth & Eurorack components
 * Cabintech Global, LLC.
 * Digi-Key – Very wide range of analog and digital ICs, including exotic types. Mostly specialized toward computer and digital electronics. Accepts small hobbyist orders.
 * Futurlec – Limited range but very good prices on many items. Occasionally very slow shipping. Ships international. Check regional sites (.au etc) for different prices on some items.
 * Jameco – Hobbyist-specific distributor, has small ranges of parts needed for analog designs but a very wide range of power supplies. Accepts small hobbyist orders.
 * Love My Switches
 * Micro Fasteners
 * Mammoth Electronics – Similar to 4site
 * Mouser – Probably one of the best parts distributors today for analog-electronics manufacturers. Very broad product range, excellent selection of audio connectors, capacitors, potentiometers, knobs and switches. Accepts small hobbyist orders.
 * Music From Outer Space – Includes electronic components.
 * Online Components – An authorized online electronic components distributor similar to Digi-Key.
 * ROHM – Designs and manufactures integrated circuits (ICs), semiconductors, and other electronic components.
 * Small Bear Electronics – Guitar pedal focus but many rare/hard-to-find parts at reasonable prices. Very fast shipping. Very good reputation. Ships international.
 * Stomp Box Parts

Obsolete, surplus and new old stock

 * All Electronics
 * American Science & Surplus - have a lot more than electronic components.
 * Anchor Electronics
 * Antique Electronic Supply
 * BGMicro
 * Deep Surplus – Excellent low-cost audio and computer cables.
 * Electronic Goldmine – A varied range of new and surplus parts. Will only ship to a small number of international countries.
 * Excess Solutions - formerly HSC Electronic Supply
 * Hamfests and Conventions
 * Twisty Wrist Arcade and Pinball Parts

Vintage synthesizer components

 * Syntaur
 * Synthparts
 * Vintage Planet
 * Utsource

Parts search engine across multiple distributors

 * Octopart
 * OEMSecrets
 * FindChips.com
 * SamacSys Ltd electronic component search engine

UK

 * An extensive list of suppliers, not just for electronics, on London Hackspace wiki.