If you want an original poster, you may check ebay.com or Amazon.com. Or do an online search. Assuming you have already done this and are being persistent, with no results, you may also check with a local book or poster shop which specializes in antique and rare items. If they don't have one, they should be able to find one through their own resources.
If you want a good quality print, there are online poster and art print sites, such as the links listed below, where you may purchase a framed or unframed print.
There is a site that is devoted to vintage and original movie posters. www.cinemasterpieces.com/ has posters for every movie imaginable, such as old Star Wars posters and Indiana Jones posters.
One can buy film posters online from a variety of stores. These stores include, but are not limited to, Movie Poster Shop, Poster Gully and Movie Poster.
form_title= Movie Posters for Sale form_header= Show off your favorite movies with a poster! What movie posters would you like?*= _ [50] How many posters do you want to buy?*= {1, 2, 3, 4, 5, More than 5} Do you want the posters professionally framed?*= () Yes () No
Movie posters need to be bought in order to be owned, though if you are lucky or search around, you can probably recieve a free poster from special movie events.
buy it on eBay
Purple is the best answer.
there are afew listed on ebay
can I buy popped popcorn in purple color from you and get it tomorrow.?
You can buy them at many different places. One of them is: Posteritati Movie Posters in the Neigborhood of Soho, Little Italy, another one is Artful Poster Ltd at Greenwich Village.
You can buy posters in lots of magazines online.
You can try checking www.ebay.com, they probably have some good deals. You can also try www.amazon.com, I get a lot of good deals on posters there as well.
eBay and Amazon have great offers on large posters from old movies, especially if you are looking for real collectible original movie posters rather than new reprints.