I'm afraid I can't help much. There used to be a nice hobby shop called Hack's of Annapolis right in the downtown neighborhood, but it's been gone for some time.
Here's a link to a hobby shop locator: http://www.hobbyretailer.com/
If you have any interest whatever in ship modeling, your prime destination in Annapolis needs to be the Naval Academy Museum. Of particular interest is the (relatively) new ship model gallery in the basement, where the priceless seventeenth- and eighteenth-century models of the Rogers Collection are exhibited. Next door is the Naval Institute Press bookstore, which will be happy to sell you so many outstanding books that you won't have any money left to do anything else on your trip.
One other suggestion for anybody traveling to the Washington area. Due to a massive renovation, the Smithsonian's National Museum of American History is scheduled to close for three years beginning sometime in September. If you want to see any of the outstanding exhibits in that building (including the new one on the history of American wars), now's the time.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.