Wizards of the Coast Inc., the manufacturer of trading card games and role-playing games, will close its chain of 64 retail stores in 15 states. Wizards, a subsidiary of Hasbro Inc., announced Sunday that the closure of its Wizards of the Coast and The Game Keeper stores will allow it to focus on its core business of game design. Wizards' games, which include "Magic: The Gathering" and "Dungeons & Dragons," are among the biggest brands in the hobby game industry. The company has retained Gordon Brothers Group LLC of Boston to assist with the closures, which should be completed in about 60 days.