The Bureau of Engraving and Printing sells them through the official government website, priced above face value as collectibles. Every note can be cut out and spent. Handing the whole sheet to a cashier is also valid, though they will silently curse you.
Credit: JFitz717
Maybe you’re thinking of a coin purse?
Any time I put coins in a billfold I make it rain like the world’s stingiest pervert.
My wallets always had compartments for bills, coins, cards and IDs