Here are a few ways of searching of images that have been licensed using one of the creative commons licenses. First one can use google to search for such images from this link, http://googlesystem.blogspot.com/2009/06/find-creative-commons-images-in-google.html and next you can do a similar search on flicker from here, http://www.flickr.com/creativecommons/by-2.0/

Other sites include http://commons.wikimedia.org/wiki/Main_Page and http://wiki.creativecommons.org/Image which contains links to still other archives of cc licensed images.

And for inspiration here are a few sites that focus on advertising. Adaccess http://library.duke.edu/digitalcollections/adaccess/browse is a searchable archive maintained by Duke University. Coloribus http://www.coloribus.com is a large archive of advertising in print, tv, and radio. It has a searchable archive but the first page of results are only viewable without subscription.

And a collection of English perspectives on china, and chinese media/advertising, http://www.danwei.org/blogs/model_workers_eng_2008.php and
http://jeanneboden.typepad.com/jeanneboden/advertising/

And lastly some blogs that offer collections of older advertising and poster design, http://www.iisg.nl/landsberger/ provides a collection of Chinese propaganda posters. http://pzrservices.typepad.com/ contains vintage advertising of all kinds.