You can get keyboard mods that allow an external keyboard (either PC or A4000 keyboard) and these connect to the motherboard keyboard header where the ribbon cable fits.

And you can also get a Keyrar device which connected to the A600/A1200 keyboard itself and allow you to use it as a PC keyboard. This is cool if you want to turn an Amiga case/keyboard into a PC by fitting a Mini-ITX motherboard inside, then from the outside it looks authentic.