thats a pocket square for sure..and yea you could prob buy them from moores, the bay, or any place that sells a lot of suits.
also, pocket squares are not handkerchiefs (looks vs actual use)
i recall that picture is from gq, and i also remember they suggested this site before, and i had it in my bookmarks for awhile and almost forgot about it (they have pocket squares):
http://www.thetiebar.com/