You can try to contact him by e-mail, he often answers rapidly.
We cannot post sources publicly as it goes against the rules.
There are plenty of Polish sources that sell to individuals. My advice would be to use the Yandex search engine and type "azotyn sodu" (it's Polish for "sodium nitrite") or "NaNo2" (SN's chemical formula) in the search bar.
After a few posts of yours, the forum's search bar will eventually unlock and you will be able to type keywords in order to find information.
Same with PMs, the function unlocks after a few posts.
Everybody here will advise you against such a method as it is highly unreliable, extremely painful (your organs shut down for an unbearably long time) and has many short- and long-term risks for your health without guaranteeing death at all. Check out atheistjoe's very informative thread, and I suggest you take a look at this thread as well:
Non-methods that should not be attempted.
If you have any more questions, feel free to ask!
Best of luck.