You can get a good number of proper "British" things if you bump across the northern border. When I had to leave for the 18mo while my visa process was playing out, DH, a Brit, was delighted to find things like proper chocolate and reasonable dairy. He delighted in making sausage rolls while we were there, too. Unfortunately, he never did manage to perfect the Yorkshire pudding at altitude with a wonky oven that didn't seem to heat evenly.
In the US, he's ordered from https://jollyposhfoods.com/ to get some proper sausages.
Me, being Canadian - my kids just came back from visiting their dad and brought back their favourite granola bars and brought me some Moritz Icy Squares. I've commandeered a cookbook from an expat Canadian who wrote all of her recipes for expats, sourcing available local ingredients to mimic a taste of home. I will say that Nanaimo squares require Bird's custard and not vanilla pudding, irrespective of what any recipe says!