Last month, Dutch journalists conducted an investigation into Nembutal scammers. The Dutch police have identified nearly 300 websites claiming to sell Nembutal, all of which are, of course, scammers.
The journalists also interviewed Exit International. They state that currently, there is no reliable seller.
The only apparent option is to go to countries in South America. For those who cannot afford a veterinarian, obtaining Nembutal seems to be a way to euthanize seriously ill animals.