This article is from the Libraries FAQ, by Anthony Wilson firstname.lastname@example.org with numerous contributions by others.
Threads on mouse ball theft have appeared on a number of library
discussion groups. Replacement mouse balls can be purchased from:
Argonaut (800) 322-3328
Prefix (800) 264-2530
Synaptech (800) 617-7865
Different vendors may have different sizes, so check to make sure that
you get the right ones. Prices seem to run $3-5 for replacement balls.
Possible solutions (from a thread on web4lib):
-Mitsumi 9-pin serial mice run about $8 (less in quantity.)
-Glue mice closed with Crazy Glue. Mice cannot be cleaned, but balls
are easily stolen and not so easily replaced. The library might still
come out ahead.
-Use touchpads. They're low in price and have no moving parts. Access
to the trackball is only through the bottom and the trackball housing
can be mounted to a desk with removeable screws.This would prevent, or
at least deter, theft of the ball.