hmm have you tried the equirey or however you spell that. they will have lists of boarding barns and phone numbers. also do a forum search.
Flat Iron Farm, A Moment in Time, and Holly Point do hunters in st. mary's county. Begin Again Farm does dressage. Looks like theres a Reverie Acres that does hunters in Calvert. Persimmon Tree Farm is a bit farther north, they are hosting a George Morris clinic so they must be good hehee. Loblolly Farm is in Hampstead (wherever that is..), does H/J.