Not much I'm afraid...

There used to be Walther's Gun Chamber and that had some nice doubles, but that closed several years ago. Accross the Bay is Albright's Gunshop in Easton, some nice stuff, high prices. There is a Basspro by the BWI aiport, but last I saw that did not have a fine gun library.

PG County shooting range is not that far away, though closer to Washington than Baltimore. Also some nice clays ranges on the Eastern Shore: Pintail Point, etc.

Hope this helps!