Ok, here's what you do.

Buy a bottle of olive oil and a bottle of vinegar (a fancy vinegar if you want, apple cider or balsamic, but not malt) then buy a packet of Italian spices (typically a blend of oregano, thyme, etc...)

Buy some salad greens, either a head of lettuce, or a box of spring mix or similar blend of greens.

To make salad dressing mix two parts oil to one part vinegar, put in a pinch of Italian spices, a pinch of salt, whisk.

Then pour over your greens, add some feta cheese olives and baby tomatoes, capers if you want.

It is a big supermarket thing moreso than a city thing. It’s a big part of the Whole Foods strategy, and an increasing part of Safeway/Ralph’s/etc. They have an increasing amount of hot food that you can take away. Walmart in the “country” didn’t, I don’t know if that’s a Walmart thing or a country thing (they did have a subway in-store).

Yeah, large supermarkets tend to have salad bars, suburban or urban. Wal-Mart has grocery items, but you're not going to find a salad bar at one. Same goes for Target. You're also not going to find a salad bar at a Trader Joe's or an Aldi's.

But your typical large-format grocery store will have one. It's hard to talk chains and be comprehensive because American supermarket chains are not national. But whatever your market's equivalent of Wegmans/Publix/Kroger/HEB/Meijer/Albertsons/Hy-Vee should have one.

There are, it should be noted, places in the US where there are not readily-available supermarkets. But those tend to be urban and rural, not suburban:

https://en.wikipedia.org/wiki/Food_desert

When I'm in the mood for a good self built salad I go to the hospital cafeteria near me. They charge by weight and have a large selection. I find most hospitals are the same. Maybe you should check out that option.