where can I find an early 1920's mark?

Question

You know, the ones that were worth less than the paper they were printed on.

Answer 1

Most coin shops will have them in their 25 cent bargain box.
I would be very surprised if you don't have a local coin shop that will sell you an example for $1 or less.
If you are in a major US city, I may be able to recommend a coin shop to check with.