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
As I heard it, he’d perforate sheets of two-dollar bills and tear them off. People nowadays might not even know there are two-dollar bills. Jefferson’s on 'em. Their circulation has been been in decline for decades because it’s simpler to use singles. So a smirking engineer ripping out a fresh rectangle of printed cotton started a lot of tense conversations.