If you are interested in a specific poster, you could venture to http://www.gigposters.com locate the poster you like and contact the designer . . . they may have copies for sale.
heh, i really wanted a 2004 winter tour poster, but didnt have the cash in halifax, but as luck would have it, i saw one on the street on the way back to the car after the gig !! ripped it off the wall with only minor rips