I'm referring to the hat that has the same finish as a normal fedora, just without the crease; not the flat hat with long fur that Satmarers wear or the higher flat ones. Like the one Rav Auerbach shlita is wearing.
Google brings several results:
Goorin Bros. Hat Shop
181 Bedford Ave, Brooklyn, NY 11211
5101 New Utrecht Ave #1, Brooklyn, NY 11219
They even have a website (not listed on the Google entry) which you can see here. You can take a look at the numerous hats they sell as well as order online.
366 Kingston Ave, Brooklyn, NY 11213
Hope this helps. Somebody who actually lives in Brooklyn could tell you better.