Hooking a PC keyboard to my TI?USB: http://ti994a.cwfk.net/TiUsbKeys.html – boards and assembled units are available here:
PS/2: http://www.harmlesslion.com/cgi-bin/showprog.cgi?search=adapter
Rave99 XT keyboard interface (no longer made..) http://mainbyte.com/ti99/hardware/rave/keyboard.html