Update: Forum member TooMuchDew sent over a bunch of links to the PDF files for all 8 of the LEGO Harry Potter movie posters:
Links to PDF Posters for Movies 1-6 are here:
I did some a Google advanced search within the domain:
and found the PDF files for all 8 movie posters (7.1 and 7.2 are bottom 2 links in search)
LEGO Harry Potter 7 - 'Deathly Hallows Part 1' movie poster:
and LEGO Harry Potter 7 - 'Deathly Hallows Part 2' movie poster
There may have been some legitimate way of arriving at the posters as a reward for playing an online Harry Potter LEGO game but I didn't bother checking.
flickr-user Okay Yaramanoglu (okayaraman) uploaded some Harry Potter movie posters stylized with LEGO minifigures in place of the actors. He CLAIMS to have gotten them from the LEGO website, but I couldn't find them on there, so he may just be lying.
Or I fail at the internet.
Deathly Hallows Part I movie poster above, Part II below. Pro is not enabled for his account; hopefully, he can comment on the forum thread and link to the original size.