The only one I know of down in MD is the Restless Lady who I believe is out of Ocean City. While I’ve never fished with them they are tied in with Canyon Runner who is one of the best tuna charters in NJ. They share information and are out pretty much everyday during the summer which gives them good info on where the fish are.
Based on our season this year the tuna fishing was best in May through July while the white marlin fishing was insane the last week of August into September. The fall tuna chunk bite never materialized so if your gonna go I would go in the early summer unless you are specifically targeting white marlin.