Our local Party City has sold out of the Disney Princess ones twice.
Our local Wal-Mart has sold out of the Disney Princesses and the classic Disney characters.
Other local stores never carried them, even though people have reported them at their stores (Walgreens, Hallmark).
If you're searching online, keep in mind that the Disney ones are not made by the official Silly Bandz company. You can search for Disney Bandz. If you search for Disney Silly Bandz, they may or may not come up. They are "character bandz" made by Forever Collectibles.
If you order online, make sure they are in stock. I believe the official release date was supposed to be July 15, although many places have been selling them for weeks.