To help me decide the fate of my Atari Basketball, I am asking if there is any interest in here in 4" trackballs. They do roll freely, but the rollers are very worn down, and they need the replacement rollers, which cost $20 for a set. They have the optic boards, which are untested at this time, but I can test if they are compatible with Oscars mouse hacks.
There are the 4" Atari "Maxi" trackballs, used in Missile Command, Football, Basketball, Soccer, and perhaps other games as well.
So, if you are interested in one, then make an offer here.