Getting your hands on cyanide pest control products would seem to be a lot easier and cheaper (not to say that it's easy these days, just easier), and lab-grade cyanide is available (it's a restricted chemical, but probably still an easier route than getting your hands on US government poison traps).
That being said, cyanide poisoning is reportedly excruciating. At least it's fast, if you take enough, but are you sure you'd get a fatal dose via aerosol dispersal from a device used against coyotes, even if you could get your hands on one?
To actually get your hands on these bombs is going to be difficult, probably as much as getting N. Also, I do not believe cyanide allows for a very peaceful death.
We dont need to get our hands on one of these in a "go buy one" sense. Research where they utilize these products, and go exploring. They have to place these traps in the wild, with little to no human interaction.
It wouldnt be painless, but its a method. No one said dying was going to be easy. Every method requires some form of legwork. Every method has a chance of sucking horribly until you die. But if you NEED to die, this is an option. People redpill the shit out of methods that arent painless, simple, or cheap. We're talking about life and death here, and we arent living in Futurama's suicide booth era. There are risks around every corner. If you have chronic pain, or other health issues that cause discomfort....are you going to say :" No, this hurts a little. Its not worth dying to, even if every day is a 5 out of 10 on the pain scale, moments of agony are just too much. " No, there are more diginified solutions, but some people must resort to undignified options when youre against the wall.
And finally, I doubt these traps are 1 pump chumps. Trigger it a few times, Im sure you'll be fine. They arent just for coyotes, so its possible its a decent dose. If they're for 30-50 feral hogs( sorry had to cash in on this one), probably be more than enough for a person.