Where can I buy a poster of the Victor Brauner painting "Prelude to a Civilization"?

I am not sure that you can. The painting is in the collection of the Metropolitan Museum of Art, and they probably hold the copyright. A reproduction of this picture In the form of a poster is not for sale in their shop. If you want to check: a href="http://www.metmuseum.org/store/st_category_browser.asp/categoryID/{E257A602-EDD5-11D2-9C16-00104B6AC573}/FromPage/catPrints" rel="nofollow"http://www.metmuseum.org/store/st_catego…/a