Fancy cast wheels don't accept the traditional wheel weights, so there are stick-on weights available. I bet you could get a couple for cheap or free from your local tire place. Alternatively, Hunter Fans used to issue its fans with a balancing kit that included a thick, heavy tape for balancing the fan blades. You could contact a store that sells ceiling fans and see if they have a fan balancing kit, but I bet you'd have to spend actual money to get one of those.