I would recommend that you try the state archives and the law library in Annapolis. They are across the street from each other on Rowe Blvd. If you need assistance, the archives is the place to start. The law library has a lot of Maryland genealogy reference books.
Also you can try the Prince George's County Genealogical library which is open on Wednesdays (better check to make sure). They are located on Tulip Grove Rd. in Bowie.