I'm not aware of a real high-end market outside of London, so I don't know if charging twice as much as everyone else wold get you any work in Scotland. $500-600 is ?250-300, which I think is unlikely to work as an hourly rate, but who knows, maybe with the right marketing it could be done.
Touring is pretty common here, so there are touring boards. Apparently Punternet is the most popular for that (brace yourself, there are some very unclassy ads there). Punterlink and puntingzone also have touring boards. You can also put up a profile on adultwork based in Edinburgh, and you'll show up as new to the area which will get people's attention.
To make a US phone work in the UK, you need a triband or quadband GSM handset and a contract which allows international roaming. If that doesn't make any sense to you, you'll need to ask your provider. They probably have something on the website dealing with the issue. If your phone is prepay, it's highly unlikely that you'll be able to roam internationally.
You'll want a UK phone if you decide to work independently, you can order one for ?15 from Virgin.