I ran out of my favorite HP Sauce and none of the local markets seems to be stocking it, so DH and I decided on a trip to British Delights in Westford, MA. They are a mail order fulfillment for all kinds of British items and have a small store that is open to the public.
We found HP (bought 2 of them) and all kinds of candy and other Christmas-y things.
If you are a fan of Cadbury, Christmas Puddings, Walker Shortbreads, Marmalades, Bangers, Puddings or other English foods, it is definitely worth a trip.