LOL
We have refrigeration, you know, and planes and trucks to transport produce all over the country to supermarkets.
California is a leading producer of fruit and veg, and Americans get the benefit of proximity to Central and South American producers, too. Arizona and Nevada are not among the more populous states.
Now that winter is upon us, I'm looking forward to seeing Texas pink grapefruit in the shops. American-grown Clementimes have already appeared. We've just had apple season, with lovely apples from two nearby states in all the shops, and before that we had melons, blueberries, raspberries, and cherries. They're all still available, but produced in California, Peru and Mexico at this point. There are lots of fresh root veg and green leafy veg too.
I live in a big Midwestern city where winters are long and cold. The local Farmer's Market operates from early May to the end of October, and takes food stamps as well as cash and card payments. I grow herbs, tomatoes and peppers - both sweet and hot - on my deck, and my downstairs neighbour grows zucchini in a little bed she created in the back yard. I bring the herbs indoors in winter and have rosemary, sage, basil, mint, thyme, and oregano whenever I want. My parish church has a 'gardening for our sisters and brothers in need' programme where parishioners donate garden crops to a city food bank. I don't grow enough to make much of a difference to the total, but every little bit counts.
I doubt there are pick your own farms near every British city and town. The SE tends to be very well served by businesses benefiting from the generally higher incomes in that region.