For classic movie posters, the premiere place in New York appears to be a store called Posteritati (www.posteritati.com). Excellent posters for the collector though their prices are really out there for some items. They seem to get posters in all the time but right now only have a belgian poster of Welles' Macbeth.
Thank you for the reply, but you are right about the prices at that place. Way too expensive for me. One purchase would ruin me! For the serious collector it is the ideal place, but I'll settle for a reprint.