It seems that there are several suppliers of Nils Poll hats, but no one definitive source for finding every possible model and style. Just check out some of the juggling supplier websites in the U.S. and Eurpoe. Such as:
http://www.renegadejuggling.com/Web_...v3k/index.html
http://www.dube.com/hat/bowler.php?cd=bowl
http://www.kineticjuggling.com/happy...-hat-p-39.html
http://www.passepasse.com/hats-c-74....b0766a52f20a91
Also, you might want to try a Dube hat, which is similar.
They can be a bit difficult to locate in exactly the size and color scheme which is most personally desired. Jugglers usually know where to get them, though, So ask around.