not sure where you are from but check somewhere like Fry's electronics. In my travels with the military, there always seems to be some type of super electronic stores, you just need to look them up.
radio shack...well sux, their selection sux, but at least they hire people that know nothing about what they sell

anyhow, in case you don't know, the yellow and green wires on the trackball are the "y" optic board, the blue and purple are the "x" optic board the red 5v and blk gnd for both boards wire to common pins at the molex that plugs to the PCB.