I kind of doubt you’d find them here in West Virginia, either. It’s not exactly a Mexican food mecca.
What about turkeys?
In Mesoamerica, they did have domesticated turkeys. You’re right. That’s still not much compared with the selection that European peasants of the time had.
This is, I think, slightly misleading, it that it implies there’s something special about eating beans and corn together in the same meal. There’s not.
Combining beans with rice or corn is esthetically pleasing and provides a nice balance of protein heavy (beans) and calorie heavy (corn/rice), just like combining beef with potatoes, but there’s no nutritional benefit from eating them together, as opposed to separate meals.
Wiki cite, since I’m time-limited: Protein combining - Wikipedia
Nor is Tennessee but I’ve seen them in the the locally owned and working class grocery store that my parents shop at. If a grocery store has an “international aisle”, they’re practically guaranteed to be stocked.
Being in Chicago, I’m confident I can find some. I know that, literally, every supermarket (okay, Aldi excepted) has them fresh in the produce department. I keep picking them up and then setting them back down again 'cause I don’t know what to do with them. Do I peel them before slicing them? How, exactly, does one peel a cactus?
…and now seeing two very different things under the name “prickly pear” makes sense - the pad AND the fruits are edible! Huh. Who knew? (Besides several million Mexicans, of course. 
)
The pads of the Nopal cactus, cut up & cooked, are called nopalitos.
The fruit is called the tuna. (Not to be confused with the fish, atún!) San Antonio’s Zuni Grill macerates tunas in tequila to make the famous Cactus 'Rita. (Shouldn’t that be Tunarita?)
I’ll give the article’s author the benefit of the doubt, even though that table didn’t cover corn or beans (or nine of the amino acids) and shows a deficiency in lysine. I’m glad I don’t have to get by on nothing but brown rice (or beans, or pumpkin, etc.), though.
Mexico is a pretty big country. People near the ocean eat what is available near the ocean. People inland eat what is available there.
Also, it is a labor-intensive cuisine. The ingredients usually do not cost very much, but it takes a lot of time to make some of the dishes. Rice and beans are cheap accompaniments to something like tamales, which are so time-consuming they traditionally are made only at holidays and sometimes include the entire family in production.
I’ve found 'em fresh and canned in da UP. If that’s true, I’d guess there’s a chance you’d find 'em anywhere.
Carefully.
Short story, I thought. IIRC in Spanish the prefix “re-” is an emphasizer which in this case means “thoroughly” or “extremely” and frito is fried - so refrito is “thoroughly fried”. When translating that into English, they transposed the prefix re- even though it had a different meaning, to get “refried”, which in English implies “fried again”.
Why grow rice if you can grow potatoes? potatoes are more nutritious, are easier to grow, and tolerate lower temperatures than rice. Rice has to be hand-transplanted, and grown in water-a lot of labor, and processing the grains is also labor-intensive. Harvesting potatoes? Just dig them up!
The mystery is why rice is so prevalent , even in climates where potato cultivation is easy.
Posole aka hominy. Granted, Mexican and New Mexican food are different (and NM is different from Tex-Mex), but posole is a relatively common side, and is often served with red chile.
I thought you serve rice with Tex-Mex (and curry) for a simple reason. Its bland. Spicy food would be too overpowering without a bland side dish to counter the effects.
Probably because you can get three or four crops a year out of a rice paddy.
If you’ve got a climate where it doesn’t get very cold, you don’t have to worry about cold tolerance. Except for some mountainous regions in the north, most of Mexico is at least USDA hardiness zone 8. Cold tolerance is not a major problem.
If you’ve got lots of available cheap labor, you don’t have to worry about rice requiring more labor. Mexico has and has had that.
Rice, especially white rice, keeps longer than potatoes.
An order of tacos around here will come with your choice of meat (fajita, tripas, pollo, etc…), cilantro and onions with sides of charro beans and a loaded baked potato. Complete with crunchy fake bacon bits. Jalisco-style Tex-Mex. Yum.
How about the chips and salsa thing? In my (limited) experience you do find those in restaurants in Mexico; is it an indigenous thing or imported from America for the comfort of tourists?