Hi Rebecca,
Character meals are your best bet without a doubt for both of these characters.
Special Agent Oso can be found during breakfast and lunch at the
Hollywood & Vine restaurant in Disney's Hollywood Studios along with Handy Manny and Leo & June from the Little Einsteins.
The Mad Hatter can be found during breakfast at
1900 Park Fare restaurant in Disney's Grand Floridian Resort and Spa along with Alice in Wonderland, Winnie the Pooh & Mary Poppins.
Reservations for both of these character meals can be made up to 180 days in advance online
HERE or by calling (407) 939-3463. Due to the popularity of all character meals, advance dining reservations are strongly recommended.
Wishing you a magical trip!