I can't help with location, but wanted to warn you that - if you do find English chocolate - it is likely to be ridiculously over-priced (since they have to import it)...
You might want to take some supplies with you or, better still, try some of the local chocolates. Ok, it is different, but one of the nice things about holidays is trying new things.
Also, if you do find 'English' chocolate make sure it is imported & not made under licence in the US as this would just taste like Hersey's in a Cadbury's wrapper!
You can definitely buy UK chocolates in the UK pavillion at Epcot. It's a bit out of the way for a special chocolate trip though! Unless you were already in Epcot, of course.
As mentioned above it is pretty pricey too. I have a very vague recollection of a Double Decker being $2.50??
I know Mandymouse (and probably opthers too I'm sure) will know so let's hope they see this post
My DDs don't miss UK chocolate in the least - they don't even ask for it as they are so busy trying all the other lovely things you can sample
I am also a big Cadbury's fan - but visit Ghiradelli's every day in the Disney Market Place either for the ice cream sundaes/malts or the chocolate itself. Best at the end of the day after a good meal. Fabulous.
The place that does internet access at Buena Vista Outlets (on 535) also sells UK chocs - not sure on prices but they certainly smelt good and the Internet prices were not bad either!
Publix sell it. And Robinsons juice at $3.99 a bottle, Colemans English mustard, baked beans and other such delicacies. There's a Publix near Vineland Outlets just off I drive.
I agree with Graeme , all the Publix's have an 'ethnic' section where they sell Heinz Beans, PG Tips, Chocolate etc - at least double the UK price, however there are certain things like Tea that they don't particularly do very well over there.
Guess it just depends on how desperate you are for the item in question.
You also have the 'Union Jack British Goods' shop at Old Town in Kissimmee, this place sells UK groceries, chocolate, crisps, tea etc - it's almost like a mini supermarket.
Prices naturally expensive.
We actually took a big bag of Cadbury mini bars and mini Easter eggs last time. We left one bar each day with the mousekeeping tip and ate the rest!!! A taste of home!