There is a place called 2A Sales (2nd Amendment Sales) in the Jessup area, close to Laurel. It is just north of Rt 32 on US Rt 1. It's not exactly College Park, but it seems like a nice shop from the times I've been in there. The owner's name is Mark.
There's a place called The Gun Rack in Burtonsville on 198 just west of US 29, but I don't really know about their prices or service. Never stopped in.
That's all I can think of in that area. I live in Baltimore and I'm much more familiar with the shops closer to here.
ETA: Both of those places are within 15-20 minutes of College Park.