JD sent in a tip pointing us to The Magazine - Not For Adults, which claims to have a poster for Harry Potter and the Prisoner of Azkaban in their October 2003 issue, on newsstands now:
I just found this Canadian kids magazine web site which says it will have a POSTER of the new AZKABAN movie. I don't know if it is true, but here is the link, scroll down until you see Hillary Duff's head.
The magazine is available at A&P and Safeway stores in Canada. Update: The editor of the magazine contacted me to say it is not an official poster and offers this description:
"The poster is from the upcoming film, as WB are one of our sponsors. I believe it ran in a Time article a few weeks (months?) ago. It shows Harry, Hermoine, and Ron peering around a brick wall. Hope this clears things up."
The image in question is indeed one of the previously released images, seen here. The Magazine - Not For Adults respectfully requests that readers do not call inquiring about the poster. Please purchase the magazine if you'd like to see a copy!