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
There are probably 0 cashiers who will except this for a sale of goods lmao
That’s why you go to a sit down restaurant, leave an appropriately large sheet behind, and walk out.