http://poisonswi2r24aznfp32sbbr3ev6ivmkkklmlgputikvkfwdohugrpqd.onion/shop.php
I don't deal in such substances, and it's not advisable for you to seek them out either. Instantaneous poisons include Novichok, cyanide group poisons, strychnine, batrachotoxin, and curare poison. Slow-acting poisons include ricin, heliotrope downy, and digitoxin. These are the ones suitable for your purposes.