There is a Milwaukee Rebbe… Rabbi Michel Twerski who is also known as the Hornisteiple Rebbe. Interesting to note, that the Steipler Gaon (born to a chasidishe family!)was from the same city!
You want to know why there really arent too many rebbes named for American cities? Well, Chasidisism sprouted in Europe and the rebbes became rebbes of specific cities. If someone like the Satmar Rebbe is from the Satmar dynasty why should he call himself anything other than that name?