Only A sells N and it's very legit.
If there is any listings on the darknet, they're likely to be not what they claim, I wouldn't trust it and I've used darknet for about any other type of drug. Over the years of buying drugs online, I've never found anyone selling N or other barbs. Not that I would ever trust it, given the nature of how rare N is... just as I wouldn't trust anyone claiming to sell quualudes.
However do be careful when contacting A and make sure the email address is right, there is scammers out there that have similar emails; so really take note on that.
Lastly I know of people who have gotten their N also, people from this forum etc. I also made an order with A but not going into specifics about my own just yet, however I will update in time when I see the timing is fit, as I still have some questions I need to ask on here about it.