It'd be cool if once every 300 strokes or so, you found a ball.
You could even make these balls be already worn-down some... maybe 20-80% condition. (If it would be hard to add in the ability to have more than one ball of the same type with worn condition, then just add this 20-80% condition to the pre-existing partially worn ball, and if it goes past 100%, then add a new ball with the remaining condition.)
If the ball wasn't good enough for your liking (e.g. a ball that normally costs 40 credits/sleeve, inferior to the GI-SD's that you play), you could choose to discard it.
If you liked the ball, though, you could keep it.
Adds to the realism and makes those without credits happy that they
found something, which they would actually use since they probably use
the standard balls anyways.
This should take all of 30 minutes to program, so it seems like a pretty reasonable addition.