There are a number of stores/galleries in NYC (and other cities too, I'm sure) which handle original posters of all kinds. However, even if you were to find an original poster from "Primrose" my guess is that it would cost far more than you would be willing to spend. Vintage posters are marketed and priced like original art - checking auction catalogs will confirm this. This is not meant to discourage you in your search - who knows, you might get lucky!