http://arts.pgparks.com/2280/The-Prince-Georges-Publick-Playhouse This link will take you to the events at the Playhouse, from there you can select what you want to purchase tickets, or at the Playhouse an hour before the event.
They have a Box Office when you enter through the main lobby
Call them.
I've always purchased them from the actual theater anytime before the show's date.
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