There were a number of black powder gun smiths in central PA. Some concentrated on particular types of repairs.
Here is a few names, don't know if they are all still in the business.
Jim Culler at Ft Chambers Gun Shop, Scotland PA Right at the I-81 exit
Dixon's Muzzle loaders Kempton PA
Brad Emig, Cabin Creek Gun Shop, Hellam PA
Bob Hoyt, fairfield PA great barrel machine work (Hear some folks are having trouble getting through to him, hunting season maybe?)
William J. Slusser 717-486-4817. Mt Holly I think
There are a few others that come to mind, but I don't even know if they are still alive.