There's a fair number of PA shows, York and Allentown probably the biggest, and while Timonium is not in PA it's not too far if you're in the southeastern portion of the state. Several Greenberg dates in or close to (Edison, NJ for instance) as well. Railserve and Trains both have good calendars on their websites, Greenberg has the list on their page. Not sure if there's going to be an Erie, PA show anymore, the gentleman who promoted that passed away.
If I were doing a listing I'd almost break it up into eastern and western PA and then include some just outside the state shows for each one.