Agree with zilla19. It is hard to find unlocked Galaxy S4 in stores. Most people buy them online. Craiglist - local listings - would be one way to do it if you cannot order online.
This Google local listing can be helpful as well, they specialize on selling unlocked smartphones: Unlocked Smartphones NY (you can find them by searching Google Map [FONT="]– New York for [/FONT]"unlocked phones")