Good morning, Jim;
I agree that Strauss Photo Technical Service in Washington, D. C. is a good place to try, although it has been 40 years since I was in there.
There is another shop in California, I think in the San Francisco area, that is highly regarded relative to the repair of the older Photomic finders for the Nikon F. I will check for their name and address, but it might take me until Monday to get it, if I cannot find it in one of my records here. While their work is highly regarded, it has been noticed that finding another Photomic finder on eek-bait is a more wallet friendly solution. Then again, when you get a Photomic back from them, it does operate just as a new one would, and with the protective coating they put on the variable resistor, it will continue to operate just as a new one for a very long time.