Electronic Components

Farnell supplier for resistors, caps and all electronics
Rapid they have some older style Capacitors
RS Online Farnell are out of stock use as a backup

Retro Computer Parts

Retroleum parts for Commodore 64, ZX Spectrum. Find a lot of things for restoring old machines here
ZX Renew ZX Spectrum cases, keyboards and membranes. Beautiful quality
You Make Robots and components for retro computers. Specialise in MicroSD tape devices
Mutant Caterpillar respected Spectrum repair shop, also sell some parts
The Future Was 8Bit things Commodore, and other systems. Makes the excellent Kung Fu Flash

Modern Retro

8Bit Do best modern retro controllers