Here are some links to places where you can find Akira Kurosawa related posters with which to plaster your walls — either physical or virtual. Some of these posters are for sale, while others are there just for display.
MoviePosterDB Quite a wide range of movie posters, including ones for Kurosawa’s films. You need to search with film titles, but it’s definitely worth it: there are about 30 posters for Seven Samurai alone. Not for sale, though.
Allposters.com A pretty ok range of Akira Kurosawa related posters, for sale. Note that their posters are all reprints.
FilmPosters.com The link takes you straight to their Kurosawa posters. These are authentic, original movie posters, and are priced accordingly.
Dominique Besson Vintage movie posters, takes you straight to the currently available Kurosawa posters.
Learn About Movie Posters Not a seller per se, but a source of information about posters and how to buy them. Be sure to check the “Movie Poster Database” (link in the left-hand menu colum) and do some Kurosawa related searches for information about Kurosawa film posters.