When people say 'posters' I think they refer to the thin sheets of paper that movie posters are typically printed onto. By saying 'window card' you're referring to the heavy card stock that Broadway shows use. Window card (or I've heard some people call it a 'Show Card') is the more appropriate term. There is always one booth at the Flea Market that has a long, bare table and they sell all sorts of window cards for $10 each and, for added cost, they will frame them right there if that's what you want.
"Mostly, I loved the size of these people's emotions. Nobody has emotions this size anymore. Outsized emotions. Operatic emotions. Kushemski and Vanda are like Tristan and Isolde, they're Paolo and Francesca. Nobody's in total thrall like this anymore. Nobody's overcome by passion like this, or goes through this kind of rage." Thomas, Venus in Fur