A book that might take you two or three years of hunting to find. Not as rare as "rare."
A good or service that is insufficient in quantity to satisfy the demand or need for it.
deficient in quantity or number compared with the demand; "fresh vegetables were scarce during the drought"
If the demand for an item is greater than the supply, then the item is scarce. If you want to see a movie but the movie is sold out, then the seats at that movie are scarce. In other words, there are no seats available for you to sit in at that movie.
(1) Not enough copies available to meet demand. (2) When referring to out-of-print/older comics: 20-100 copies.
20-100 copies estimated to exist.
In short supply, but with more survivors accessible than of a coin properly labled as rare.