For mid-Atlantic comps, mid June to Mid July is not very busy. Mays Landing is July 9/10. Also, Late July early August is usually open. If you are looking after Labor day, it can be fairly busy, but there are available weekend.
You need to look at the comps that draw the teams you are trying to attract and try and be two weeks away from those comps. A lot of teams don't want to do back to back weekends if possible. I would avoid conflicts with the NJ comps, Bel Air, New Holland.
I would look at the KCBS website for posted events. While all are not there yet, many are. From what I can tell, the last 3 weekends in June are open. I think this is your better choice ( 6/18,19 or 6/25/26 even though DC in the 26th). Or last weekend in July first weekend in August.
Good Luck!! Remember, you'll never please everybody no matter what date you pick.