I felt the need to reply since I grew up in Central PA! Unfortunately, I don't know many stores in PA since I didn't start this hobby until after I left PA. However, whenever I get back I try to go to
Stamp-ede in York. I know this is a bit over 2 hours, depending on where you are from in Central PA, but I like this store. You also might want to check out this
thread. It has a lot of information about stores in PA.