I don't claim to be Professor Drugs here. I kind of accidentally learned how to meth while researching North Korea while I was living in the South. Working in Asia is a bit crazy and drug charges are basically the worst thing to happen to a foreigner working there (and not uncommon given our relatively lax attitude to stuff like weed), so I educated myself a little.
Let's go with the aforementioned "meth while you drive" route, which is pretty easy but only really works on very small amounts. It's main appeal is you don't need much pseudoephedrine - so you can get around restrictions - but it also requires some hydrophobic solvents, ammonium nitrate, lye, lithium, salt and sulphuric acid. So while most of that is stuff you can fairly easily get hold of (pseudoephedrine from raiding a pharmacy; camping fuel or starter fluid for the hydrophobic solvent; liquid fertiliser; lithium batteries) and are fairly easy to get today, five years into the Crash a lot of that stuff is going to command a higher price if it's easily available at all. You try haggling an enclave out of the fertiliser it needs to grow food, or talking Aaron into letting you have his gadgets' batteries for meth. (And yes, the lithium in the batteries does mean this is one of the riskier meth process out there in terms of woops where did all this fire come from)
If your Taker group is out in the Midwest, or any area that was heavily agricultural pre-Crash, the Birch method is a bit simpler and easier to work on a larger scale. Again, you're reacting liquid fertilizer with pseudoephedrine and some kind of alkaline metal, such as sodium or lithium, and again you're at risk of burning down your everything. That's also not as bad as the Australian "hypo" method, which is fantastic if you want to inhale phosphene gas and/or get scorched by white phosphorous. This is all leaving aside the common practice of combining meth with other stimulants such as caffeine (no, really, meth isn't enough for some people).
That said, meth does have a history of use in the US military as modern as the Persian Gulf War - which Caleb alluded to which his evac sauce in episode 1 - so it's possible there are some US government owned facilities out there that were converted to ES production during the Crash. It's possible that the government did a lot of the work for you before NOPE'ing out, or falling to infection. Get past a few Casualties to get into a warehouse of liquid fertiliser, pseudoephedrine and alkaline metals? And the flammability/explosive risk the lithium/sodium imposes gives you a time limit or environmental complication on the mission because those commonly catch fire on contact with moisture or air - something's on fire, take what you can and go.
As to whether there are facilities to making chemical precursors east of the Missippi - honestly, I'd have to do some research on the industrial presences in the region before I commented. It's not a region I know particularly well. I do know that pseudoephedrine is produced from plant alkaloids, and that some of the plants in question (the genus Ephedra) do grow in America. That said, currently the majority of pseudoephedrine refinement and production takes place in India and China so once local stocks of that run out, you're probably going to have to start farming Ephredra plants to brew Mormon Tea.