Are you worried about authenticity? If not I strongly recommend jumping on amigakit.com and getting a Cocolino Amiga to PS/2 adapter. Clunky old Commodore mice are nice for the authenticity factor, but they're shocking for actual usability. I run a Microsoft IntelliMouse on mine and it's fantastic.
Just the local Commodore hobo and middle-aged PC hoarder.
eisa on Trademe. A lasting reminder of a Compaq fetish when I was younger.