As many people have observed on this site on many threads, we don’t have Mexican food in Boston of the range and quality you get in California. It’s best to temper expectations and enjoy what we have, not anguish over what we don’t.
Having said that, even in California, where I have spent time, it’s not commonplace to find the body-part-specific tacos you mention. Tongue is common (although they do not always reveal which animal it’s from), and belly, but stomach, etc., are found only in some places. And you have to really look for eyes. Even in Mexico City the typical street-corner taco stand has only 4 or 5 standard offerings. There may have been a golden age when every body part was gloriously available on every corner, but that does not seem to be the case any more.
