I don't know if you're still here. Other people might find this information useful.
Information found in List of Resources PPeH 2018
You need at least 40 250mg pills. I told my doctor I would be spending a few months in an area where this drug would work. I went to the CDC to find this information. My doctor prescribed 23 or 24 500mg.
It doesn't mention taking metoclopramide, but I know I will take it. If my shipment doesn't arrive before I leave I'm pretty sure I can get it OTC in Mexico for nausea caused by migraines.
There is some debate on whether or not Valium will help or hinder. I'm going to ER on the side of caution myself.
Barbiturates, B Blockers, and alcohol can help increase lethal effects, but the book doesn't say you have to do this. Again, I'm going to err on the side of caution and take something that will knock me out.
I'm staying away from alcohol once I start my fast. A pint of Guinness makes me a little tipsy on a full stomach, I can't imagine what a shot of vodka would do to me.
I pretty sure I can buy these pretty easily anywhere in Mexico given my medical history. Your mileage may vary.
I wish you well on your travels, wherever they may lead you.