>I'd even be willing to explore the dark web for it, but I don't know how to really.
Here anon, I originally wrote this guide for people who want to order recreationally drugs from the darknet: http://pastebin.com/4xz9RdWk
The paste will expire in 2 weeks, so save a copy as a .txt file for your own use.
As for what you should order and how you should use it to end your life, the current opiate of choice that is easily available on the darknet and is extremely potent would be fentanyl. The LD50 (lethal dose for 50% of people) is approx 2.1mg for a 70kg person.
I'd recommend ordering 5mg at minimum (if you want to be absolutely sure, order as much as you can - nuke the site from orbit, so to speak).
When the time comes, drink half a bottle of vodka (combining opiates with other central nervous system suppressants such as booze or benzos increases their potential lethality - this is probably overkill but hey, we want to be absolutely certain you die, right?), put on some nice music and then rub all the fentanyl into your gums. Sit down comfortably and then just twiddle your thumbs patiently until existence just sort of fades away without you even realising it.