There's Triple-A Hobbies, but that's in Jersey, so it's probably out of your way. AAA is the warehouse and retail outlet for MRC.
Mainline Hobbies is located in the Plymouth Meeting Mall, which is just off the turnpike, where the Northeast Extension meets the East-West turnpike. Here is their website: http://mainlinehobbies.com/
That's about all I can think of. Penn Valley Hobbies in Lansdale is still in business, but they finally stopped keeping hours at the store, and they confine themselves to their online and eBay sales. And we lost Herb's Hobbies in Doylestown.
I'm in Bethlehem. Whereabouts in PA are you? We have an old-school LHS going strong, Trains & Lanes, outside of Easton and Nazareth. Otherwise, there's HobbyTown in Whitehall, as well as a couple of Michael's locations, AC Moore, and two HobbyLobbies (one in Nazareth, and one in Trexlertown)
Best regards,
Brad