As a Mexican who has lived the last couple of years in Boston I can tell you the ingredients can be pretty hard to find: avocados are pretty tasteless here, the only variety of corn that you can by is very watery and insanely sweet, the only chilies you can easily find are jalapeños and sometimes old poblanos (which is bad, since Mexican food uses a bunch of chilies with very different tastes; I especially miss serranos and some the dried chilies like pasilla and morita), I haven't been able to find fresh nopales (the delicious fleshy leaves of the prickly pear cactus), cow's brains or eyes, zucchini flowers, huitlacoche (a black fungus that grows on corn), etc. I've found passable tortillas at least, but nothing to write home about. (If I were more highly motivated I'd just make some myself, which I know from experience would be better --I used to do that in when I lived in Toronto before Toronto got a good tortilleria-- since, thankfully, they do sell here the finely ground corn meal the tortilla masa is made of.)

I agree that plenty of Mexican food is not hard to make (specially the kinds of Mexican food I've seen people eat here in the US) if you can get the ingredients, but (1) you can't always get them, and (2) there is also lots of stuff that is complicated or at least very labor intensive to make at home, like mole. (Which I make a point of eating when I go back to visit.)

Although I have to say, I don't really get the whole "missing food" thing: if what you used to like eating isn't readily available in a new place just give up on it and figure out what's good where you are. I'd be pretty surprised by a place that has no good food at all.