Without seeing the door, we probably can't tell you for sure whether
the wheels can be replaced, but I would be surprised if they can't. If
you can get the door off and remove the wheels (and any bracket/
assembly they may be attached to), you might have luck taking them in
and matching them up yourself. Ask them what isle the parts for
sliding glass doors are on (don't say anything about a shower) and see
what you find. The HD near me has quite a selection, but I wouldn't
expect most of the employees to know any more than I can see from
looking at the package.