You can buy Disney character themed ones before your trip from a place like Party City or any big box store that sells Disney-themed party supplies/party favors (like for kid birthday parties).
They are also sold online as a create-your-own promotional item. It depends on the size and quantity. I just checked, and it is possible or order 1 for like $5, up to 1000's. If you order 25, the price drops below 50 cents each for a small one. (Then the price drops to like ten cents each for orders of 1,000+.) Could be fun to design one if anyone is planning a family reunion or some other event.