There are tons of places on the web that sell movie poster frames. After much research, I purchased frames from Wholesale Posterframes through an ebay offering. You can buy them direct through their company website to get customized sizes, or on ebay where they also sell them individually, or in blocks.
http://cgi.ebay.com/27-x-40-UV-FILTERING-MOVIE-POSTER-FRAMES-27x40-FRAME-B_W0QQitemZ110011960050QQihZ001QQcategoryZ60334QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
They ship extremely fast, and the fit and finish is excellent.
There are also a ton of places selling movie posters.
http://www.movieposter.com/
I went through this company for posters. The website is excellent because you can navigate by poster type(origional or reprint), size, price range, date, etc, etc, etc. It was much easier to find exactly what I was looking for by using this service.
PS... A word of warning. If you plan to buy the cheaper reprints, the sizes will vary and they will not conform to the standard 27x40 poster size. For example, a reprint might arrive, and it might measure 26.5x38.5 which means it wont fit your frame correctly. If you buy origionals, they will fit your 27x40 frame perfectly. Granted, if you want to buy SW, Raiders, Jaws, and other various classics, you'll need to buy reprints, just be aware that they wont be exactly 27x40. I was looking into buying some classics too until I discovered reprint sizes are not standard, so I opted for new releases instead... IE. Superman-returns, Pirates2, etc, etc.... and newer posters like that.
I bought a 4-pack of 27x40 frames, a large 30x40 frame, and five origional posters from the above websites, and the products were excellent quality, and they arrived within a few business days. These are high quality polished aluminum frames, and they'll probably cost more than a cheap Wal-Mart alternative, but they're a higher quality frame & look awesome.
Good Luck