Check this out
http://www.retouchpro.com/forums/cla...er-wanted.html 
It might be what your looking for - then again it might not, details are sketchy.
Retouchers are everywhere - not just NYC

but if you're looking for high fashion stuff, any of the fashion capitals(London, Paris, Milan, etc) will a higher concentration of studios, for the same reasons as NYC.
If you're thinking of moving, I would strongly advise securing a job here first.