Fixing a Speedometer??

My Speedometer just broke. I checked the cable and it seems fine. I have a 67 Barracuda with the 150 mph speedo.

Can these be fixed? Is it hard? Is there somebody who specializes in fixing speedos?

I have a 3 3/8" Autometer speedometer in my Dart and it looks like (more or less) the same size. Could be an option here.