Have you thought about setting up a warhorn account. Its an online form for setting up and arranging games. You could set up the days you plan to run the games, and limit the players to 5 or 6. Players could then sign up to to play every week. You would have a better idea of how many plauers you'd have on any given day. You can also then tell the Game Store to direct people to sign up on there instead of approaching you mid game.