Can anyone suggest any good Cake decorating 'supplies' shops in New York and Las Vegas, I live in England and am coming over in the Summer?

There are none in Las Vegas. There is one small shop in Henderson which is a neighboring town; however you can get better and cheaper supplies online (even with shipping costs). I always had to order off the internet when I lived there (except for the couple of things you can get at Michaels or Joann craft store)

In NYC there a cake store on 22nd and 6th called NYcake
They actually also ship international too. Thats really the only good on in the city. Pfeil and Holing is in Queens. They don't have a retail shop But call them and see if you can pick up direct from them. (I know they allow this for bulk orders... not sure if they do for smaller ones) http://www.cakedeco.com/

Las Vegas:
http://chefrubber.com/

If while in New York, you happen to be on Long Island, the Chocolate Duck in Farmingdale is great.

There is an AWESOME spot!
In the indoor swapmeet on the west side of town on Oakey and Decatur. So not where you'd typically expect to find suppllies. But living on that side of town it's pretty great to know I can get things there. They have lots of CK stuff, all kinds of cupcake liners and they have a rainbow of fave thing to use. DISCO DUST!! It's pretty reasonable prices and everytime I'm there the girls that run the booth are always super nice and helpful!
sweethouselv.com

Vegascandy, that's awesome to hear.....I'm heading there at the end of the month!
Can't wait to check it out!

Thank you for sharing Vegascandy. I frequent your city to visit my friend and we always go to Henderson because there is no other place to my friends knowledge.

Will check it out.