There used to be numerous shops in the States that sold Cadbury's chocolate imported from the UK (at huge price markups of course) to homesick ex-pats and others who would appreciate it, but when Hershey's renegotiated their contract as the official licensee of Cadbury's in the US a few years back, they got a clause inserted saying that they were the only ones who could sell anything Cadbury's branded from then on. Cue numerous lawsuits to get these shops shut down (or at least the Cadbury's products removed from them), even though the Hershey's versions were very different (e.g. terrible) or not actually ones that they were even producing for the US market anyway.
I only heard about this when I went to the United Kingdom bit of Epcot in Walt Disney World. Their sweet shop used to do a roaring trade in a wide range of British chocolate, but now has hardly anything on sale. I think Nestle allows them to sell things that aren't available in the US (so things like Smarties yes, but KitKats no) and they have some stuff from Tunnocks and other independent suppliers, but there's no Cadbury's or Mars products any more. Shame, because it always amused me to see Yanks buying British chocolate bars at $3 a pop!