The guys at Kindermann in Toronto have a lot of experience in screw mount cameras. I believe that when Leica quite servicing the screw mount stuff they bought all the remaining stocks of spare parts, so they are well equipped to work on them.

I've had my IIIc serviced by them and it came back working like a Swiss watch, which was much better than when it went in. I also inherited my camera and it had sat for a long time.