While I don't have a Cali top, while reading this thread, it made me think about this one company that makes gears for the E28 and E30 VDO Speedometers. I wonder if they could produce a set of the plastic gears or at least know of a company that can. I realize the materials are different, but who knows...
I'll search for the company name if anyone is interested.
Good luck
Update: I now have a 98 Sport with a Cali top. Same issue.