Original movie posters are manufactured by the movie studio for the film's release and distributed to cinemas and made available to buy.
They are not reproductions created at a later date or alongside the original movie posters by a third party not associated with a film's marketing.
You can find vintage original movie posters for sale at FFF Movie Posters:
FFF Movie Posters
7013 E Main St
Scottsdale, AZ 85251
(480) 429-6800
http://fffmovieposters.com