Walmart may be monolithic, but not quite so monolithic that if one store stocks models, it means all of them will stock them. But as others have said, even if you have a local Walmart stocking model kits, the selection probably isn't much to satisfy someone who has been building for a while.
Having said that, though, I'll add that the kits you might find, might be the kind of kit to give to a kid you know, to help encourage him to take up the hobby. That's probably how many of us got started. I didn't spring from my mother's womb and seek out the nearest hobby shop. Rather, when I was 5, my dad gave me a very basic kit and a tube of Duco Household Cement. From there, it was my parents and the other adults who did the same, gave me kits as presents, and as I got older, and earned money for chores, etc, I started buying my own. I went from going along on the trip to department store with Mom & Dad, and buying something myself, to riding my bike to a local store (Penn Valley Hobbies, Lansdale, PA-about 8 miles on my bike).
So I wouldn't turn my nose up at Walmart, as far as models go, but approach it from that angle.