The blank stamp pages in the SQC book? You can store any stamps on those! The web and downloaded versions are the same, and the current stamp collections are: birds, fish&critters, flowers, insects&patterns, landscapes, misc1&2, secrets, winterfest. Hoping to add more in the next update!
All the stamps in the collections book are in the game, some are harder to find ‘cause rng can be a pain. The mystery pack is your best bet for getting them all, however, we’ve added some new stuff for the next update that should make it a lot easier to find those stamps you’re missing :)