Michael:
I had held off posting to your question as I figured you might hear about something closer. Since that doesn't seem to be the case, I'll call your attention to the Mifflin County Model Railroad Club in Lewistown, PA. I know it's close to a 2 hour drive from the Williamsport area, but they are a great bunch of guys and have two beautiful layouts, one O gauge and an HO layout that depicts the PRR Middle Division.
Max and I have visited with these fellows when we have been back in PA visiting relatives in the summer. Thursday evening is their normal club work night and at least one of their guys (Forum name Forest) is a regular poster on here.
Curt