Don't know if this will help or not but over at
www.byoac.com they have a keybpard emulator for home brew arcade machines (addicting let me tell you). Anyhow, this is the one I use:
http://www.ultimarc.com/ipac1.html
It plugs in between your keyboard and computer and you can map keys for the buttons to emulate. Nice thing is you can use any kind of switch you like once it's connected.
Theres a wealth of info at byoac about switches too. Just cruise around a bit and you can find different kinds of switches. I warn you though, much like carputers this can be a bit of a black hole from whence you may not be able to return.
Hope that helps some.