What 'area' would that be? I would guess that Three Mules Welding Supply(Lex Park and Mechanicsville) would fill bottles. Cather Marine down in Colton's Point used to fill them too..might still.
Not sure if they provide refills, but there's a paintball facility in Newburg...a friend owns the company. Visit Home - Southern Maryland Paintball for more details.
Try the tackle Box in Lexington Park. The Sunoco station/small engine place on RTE 4 N just short of Prince Frederick should do it as well, they sell paint ball equipment. I think it's Mattison's but am not sure