I just found a The Three Musketeers poster for sale on ebay UK. The price is 49.99 English pounds, and there are about 5 days left on the auction (from June 30th). The postage is 5.50 English pounds, and it looks like the seller is shipping worldwide!
It says nothing about the condition. The yellowing might just be from camera flash.
Anyway, if anyone is interested in it, go to the sale here. This is a great find!