Having the vet see through your story and contact your local mental health service/police are, in my opinion, the much, much more realistic outcome. Certainly there are very dodgy vets out there, because there are lots of dodgy people full stop, so no profession is exempt, but even with that being the case, if there were any way whatsoever to trace the N back to that vet, they'd be done for. I think the vast majority of vets would be intelligent enough not to take that risk.
I'm sorry for your suffering. I wish N were accessible to those who just want nothing more a peaceful and reliable exit. But I think much more bad would come from making any attempt to buy it, than is worth the tiny sliver of potential where you might be able to get it.