This was a few years ago, but I remember Cyberweld used to sell small nitrogen tanks online. They realized there was a large amount of traffic coming from this site. So it got to the point that if you visited from a direct link on here you would be redirected to a suicide help page, thanks to the refer header info.
I don't think they carry nitrogen publicly anymore either on their site, as all I can find looking now is just argon, or argon + Co2 mixes.
There was also a controversy about them more recently, because they were selling half full, and at times expired out of date tanks. As the tanks themselves have marking indicators on them to show testing dates. If the tank gets out of date, it is deemed unsafe to have refilled; making it essentially junk.
I remember the "good ol' days" on here when everyone would just post direct links to suppliers of SN and other things. Then the ebay sellers started shutting down, and it became a lot more secretive along the way.