i'm afraid you would have to know someone or go on the "dark web" or whatever they call it, but watch out with that shit, it's some sketchy shit on there.
luckily i never visited that shit, but i saw a lot of documentaries about it.
but there are other drugs or naturally occuring substances that could work.
i hear a lot about SN on this site. it's a toxic salt.
and apparently it's pretty easy to find, legally