Hello! I bought a 2 1/4" HAPP trackball some years back. It has a small green board where things are to be plugged into it. One spot is for a proprietary USB and PS/2 combo cable. I have no clue what I did with mine! I looked for it for an entire week.
It seems like HAPP sells it at their website for under $20 but they have a $100 minimum on all orders.
If anyone has one to sell (perhaps you are using an iPAC or something to hook yours up and you do not need it), feel free to sell it to me! Thanks!