Have you tried pulling them apart and cleaning them? There is really nothing to them. What there is, there are kits to replace the bearings, rollers and idlers. Give it a try. If I can do it,anyone can.
Depends on what you need. Check Bob Roberts, he has a bunch. I've seen the bearings and rollers go for $30 a set.
I was going to post a question about trackballs later, after I take some photos. My rollers have big gouges in them from use and I can't figure out what size to get.
Do a Google search for trackball cleaning. Lots of useful info.
Did you pull it out and look at the casing? Mine had Imperial stamped on the case. There are a bunch of different ones out there. Get the manual for your game, if it's original equipment there is probably information on it in the manual.