Companies like PrimeLine make a very few "generic" hardware parts for shower doors. You find them at HD, Hardware store, Specialty glass store. In general, the odds are WAY against finding proper parts for a 25 year old shower door. If the rest of the door is in such great condition that you are willing to spend a lot of time and money repairing it, that in itself is a minor miracle.
I think a new door set is in your future!