I miss Fred Meyer

For us Wegman's has a modest British section and I will occasionally splurge on a can of beans or bottle of HP, they also carry Yorkshire Gold loose tea which is our preferred blend, Vimto comes from the little International Market that caters to foreign students, and is the Middle Eastern version without any artificial sweeteners rather than the current UK variety. We make our own bacon and sausages. Other than that there is little in the way of British food that we buy in. When I have been back to the UK I will bring a small amount back with me - a bigger bottle of HP, Marmite etc but in general we accept paying over the odds for the occasional treat and enjoy all the other good foods available over here.

As suggested above, thoroughly search the supermarkets. Some have sections, some have a few items - e.g. locally Walker's shortbread, Colman's mustard, chocolate orange.

Costco for big tins of Walker's shortbread just at the moment - they have it every Christmas, also twin packs of Lea & Perrins all year round, occasionally Warburton's crumpets (they freeze just fine).

World Market, HEB, Kroger, Amazon, Costco.... Houston area that is....

On the west coast we have Costplus World market which sells a lot of random stuff including "food from around the world" with a decent British section, even some mince pies at Christmas if you are really desperate. Also I find that many indian shops will have a small British section, PG tips, marmite, Hob knobs.. that kind of thing

Get used to US food, then the British food becomes more of a treat when you splash out or visit.

My only indulgences now are sandwich pickle and marmite, and I don't eat them that often since I don't eat sandwiches very regularly.

with relatives, get them to bring bulk Large Jars of your favourite, I like Branston and marmite, you can eek it out and make it last. However, Covid has an effect on this method, so we are going to run out.
Kroger have small british sections (in Virginia), you can get HP and tetley and other common branded things, there is also 'Foods of all nations' in Charlotesville , VA, which has a good quirky selection from all nations, i like that kind of euro shopping, I miss it, however, we do not shop there on purpose its expensive, only if we are passing through.
Fresh markets also have a reasonable Deli with some good cheeses like Gouda and gruyere, stinky munster and such, my wife is a cheese fiend so it suits her.

also, make your own home made grub, my wife is very good at that , I am lucky so and so.

Summer 2015 one of our new colleagues missed a courgette and it grew, as they do, into a marrow. Steve brought it home and I made it into chutney, it has now matured into a Branston style dark pickle which is really good.

One advantage of living in Toronto...lots of British goodies.

I find the British Food Section at my local grocery shop to be ridiculously expensive. Which is why I was looking to buy Online this time. Until the Covid Pandemic has passed it looks like I won’t be visiting home in the near future or have my folks visit me.

On a side note - if I were to buy online would I need to pay any Customs Duty?

While the cost of getting British food is significantly more than popping to Tesco, I find it easier to compare relative to local food purchases. As an example, Publix sell Digestives at $3.39 a pop, or close to that, which is eye watering. BUT, if I compare that to an over packaged Oreo purchase, they are on a par.

We use British Corner Shop for the stuff the small Publix allocation doesn't cover - again, it's more expensive than buying in the UK, but it still comes out in the wash against local food items when we buy enough in bulk. For items such as Crumpets, which are not available locally to me or suitable for BCS, then a homemade recipe is now the go to - took a few attempts, but getting close.

As much as I am completely game on getting into local foods, I like to spend on a few items that cannot be replaced. Pickled Onion Monster Munch were just eaten for lunch, as an example. Yesterday I had Cheeto's Puffs - everyone is happy.

Costco has 'em sometimes, but LizzyQ's sourdough crumpets are amazing

Are there big differences between food available in the UK and the US ? Examples !

When we first moved I noticed that many things tasted sweeter than I was used to....bread, orange juice in particular. Bread and milk lasted for weeks.

It’s the things you miss, for us it was Branston, Marmite, Heinz Beans, Mushy Peas, M&S food, PGTips, carved ham, crumpets, biscuits, Cadbury’s chocolate, Thornton’s, marmalade. Easter eggs. The list is endless,