Is there a way to fix the gears In these or do you just have to find a whole unit?

 

I don't know how you would disassemble the mirror to repair/replace the gears. Not saying it can't be done though. Use this search engine to see if there are any wagons in a salvage yard near you. I'd check for Delta 88s and 98s; as well as, other full-sized GM cars from that era.

http://www.car-part.com/