You are going to have a very difficult time finding a good beach site this close to the summer camping season, but I may be able to help....
MickeyBrennan mentioned Assateague Island SP above. We have two sites available on I-loop open at Assateague from July 25 to Auugust 4. We have a total of 8 sites in a group, but 2 families had to back out of the trip, both related to new jobs and no vacation availability.
We are right on the beachside if the loop, so bugs usually aren't as much of an issue. If you are at all interested, PM me, and I will send you details...