You mean you live in the UK, with all those lovely double decker buses that have a built-in second story deck, and you want one of OUR buses? I'd just get a double decker there and go hog wild with it. Buying a UK bus also means being able to get parts and repairs locally without having to import parts. I imagine getting a US bus tagged over there would be a challenge as well.
Don't get me wrong, get what you want, but from my perspective you'd be ording a salad in a steak house by importing a US school bus with those double deckers.