Syntax30 - I finally visited the store last weekend. It's a medium sized corner shop/news agents in Holland Park. There are 3 shelves full of american goodies, mostly cereals, cake mix and sweets, along with a collection of various sodas in a chiller.
The prices seem pretty typical for most American import places, so it's nice to get some of these as a special treat sometimes.
I haven't done the mail order, but the store is legit.