Unlike many drugs, Crystal Meth (
http://en.wikipedia.org/wiki/Methamphetamine) is not directly derived from a single plant, but from a variety of (common household) chemicals and legal medications (which can have multiple organic or chemically derived sources).
Essentially, a Meth Lab simply needs access to a pharmacy and a grocery store and a wide open space to brew them where the frequent detonations of the volatile compounds will not go noticed by the police. Hence, why it is primarily a rural drug - it can be produced without any international connections to illegal-crop-producing farms, and it requires the ability to hide your meth lab in a secluded area.
The sort of things you'd just find underground would be more like "Magic Mushrooms" (which I believe are simply dried out, no further processing needed), or some underground analogue of marijuana or opium. I believe the original source of LSD was a fungus, but it needs to be seriously chemically derived, first.
Of course, Magic Mushrooms are poisonous alongside being psychotropic, while LSD is just very, very powerful, and essentially rewires your brain (so that you "see scents" because your brain's nasal nerves become linked to the optics portion of your mind) to the point where you can cause permanent brain damage, but they aren't addictive, as other drugs like cocaine or meth or anything made from opium are.
http://en.wikipedia.org/wiki/File:Drug_danger_and_dependence.png (Note that caffine is in the middle, there)