There's an upcoming convention the Military History Weekend, in Williamsburg, VA. Brian Youse and I attended the convention two years ago, and while the focus wasn't on boardgames, we both had a good time.
The show focuses on reenactors (quite a large number of uniforms are for sale), miniature figures, and books. Osprey publishing had a very large presense there two years ago, and will be there this year as well.
More details of the concention are available here.