I designed the controller board specifically for this task, so there is a connector where the keyboard cable from a Commodore 64, Commodore 64C, Commodore VIC20 or Commodore 16 can plug in directly, as can the original power LED.
It is also available in a version with a mode switch to change mappings between normal use and the vice commodore emulator, This version of the kit also includes a replacement power LED which will light up red for emulator mode and green for normal mode.
The controller can be mounted on the back of the keyboard, and the cable fed out of an existing hole in the case.
Alternatively, it can be mounted at the back of the case, so the USB socket (and optional mode switch) can be accessed with the IEC and Video connector holes.
You can buy these as conversion kits - Commodore USB keyboard kits. Or, if you don't want to convert the Commodore yourself, you can send it to me to be converted,
Please be respectful of the original computers, and only use unrepairable computers, or at least pass on usable parts to someone that will be able to make use of them.
I'm working on a version which includes two joystick ports, and fits in the existing holes in the sides of the case. That should be available soon.
Update: Available new, Commodore 64 USB keyboard and dual joystick boards.
Also coming up, a version which will work with the original Commodore 64, so it can be used as a USB keyboard when the Commodore 64 is off, and a Commodore 64 when it is switched on.
Update: The Time Shared Commodore 64 USB Keyboard kit is here
2023 Update
USB Keyboard Controller Kits are available from my Sell My Retro store: