Thank you, like most people on here I've been struggling for a very long time and since being on this site have seen alot of talk about SN?
Welcome. Sorry to hear that life has brought you to this point. Thankfully, this is a very supportive community.
You'll want to acquaint yourself with the Resources Compilation pinned thread in this forum. You can read more about sodium nitrite (SN) there.
No one in this site will ever tell you where to purchase an item as it's against the rules. Resources exist on the site so you can view the information and make informed decisions about your future.
Depending on where you are in your life situation, the Recovery forum may be a great resource as well. Like I said, we are a very supportive community. Many people come here feeling suicidal and because of the information and network here, find other paths. I hope you find the path that's right for you.