you should check ebay. they have a lot of posters of him. they have some where he's dressed as the joker, one where he's holding a skateboard, wearing his cowboy outfit from brokeback mountain, etc.
ebay would be the easiest place, as they would have lots of them. otherwise movie/music memorabilia stores also have them, but it would be difficult to find exactly what you want
Amazon.com: heath ledger poster
