Is it possible to get replacement rollers for the quarter windows? I am referring to the rollers that go in the vertical tracks, not the one on the regulator.
If you're talking about those round little plastic bits with the metal clips, yeah, you can get 'em. Call up any Mustang shop and explain what you need. I've replaced all of mine.
I don't think they are replaceable. I think that after they were assembled, the shaft end is peened over with a press. Typically they do not wear out, just bind up. If that is the case with yours, soaking with WD40 or similar spray will help get them going. Clean them out real good, then use a spray with graphite.