I don't believe so. If I walk into a store in New York and tell them I'm from the UK, they won't suddenly become subject to UK/EU law if they choose to serve me. I'm the one subjecting myself to US law if I shop there, not vice versa.

Further, even if they were subject to EU law on this, how would any action for a breach be enforced?

But you are on US soil when you walk into that shop. There are many examples of UK firms not selling to US clients - poker firms, National Lottery...

That's my understanding.