Just to make some people think about it;

Inside of most PC Keyboard (surplus ones), you can find a single 40 pins
(DIP) custom chip. This chip contains everything it needs to scan all
the rows and columns of the keyboard and talk to the external world via
few wires, using +5V as power.  It can also lit 3 leds (used as NumLock,
CapsLock and ScrollLock). It doesn't need any crystal or ressonator, it
is ready to scan your custom keyboard and supply the info in serial way.

Yeah, ok, it is an ugly 40 pins big chip, but it should be of some use
for someone in this list looking for some answer like that. I just
wanted to make "that" person knows it, since sometimes you can get those
surplus bad keyboards (missing keys, keys not working, case cracked,
very dirty...) for free.

Wagner.