Hi Stan,
If you are patient, you mighty find a later Ford Tachometer made by Faria (Same company that made the GT350 tach) at a swap meet with the same red line dial and glass face. See image below. They are out there. Assuming the dial is good, you can just make the swap. There is also a 6K tach version with COBRA emblem with the same piece, but those are also going for bigger money these days. (You definitely don't want to buy one NOS in the box to salvage dial and glass. But they are out there too.) If you could find either one for a $100 with bad wiring or other issues, you could be money ahead compared to having the tach restored. A 6K version sold at John Atzbach collection auction for exactly $100. It needed new wire connectors.
If you give up there, you can try Phil Severance who restores these tach's. I am sure he can make the repair.
Best of luck
Cory