I would say Hollywood Studios as it would be the best place to find it since they have a bunch of Pixar related items...Second place would be World of Disney at Disney Springs..
I would have thought a Tigger tail would have been fairly easy to find on Disney property since it's extremely recognizable; after all isn't that tail an integral feature to Tigger and allows him to bounce. And I could have sworn I saw Tokyo guests eat pastry Tigger tails when I was there............but as for Sulley I'm not sure I would even know his tail if I saw one.