In Austin TX there is a supermarket at Interstate 35 and 38th Street called Fiesta -- the last I knew, they had some "International" aisles one of which carried a selection of UK foods -- candy bars, Birds Eye custard, all kinds of things. The prices, however, were definitely "luxury import" prices. A can of Birds Eye Ambrosia made with Devon cream, while about, what? 60p in the UK, cost $2.00 at Fiesta.
Also be careful with chocolate that seems to be the UK version and brand -- some of them are licenced to be manufactured in Hershey PA, are made to a different formula, and they actually don't taste the same as the UK version of the same candy bar.