SN, like other drugs and such, are difficult to get in(to) the US. You can technically buy them, but you'd need to prove you had a need business or chem wise. You can't just go out and purchase it. IIRC, things like N are easier to get elsewhere.
DMC has a lot of clout here because 1) reliable seller 2) discreet (as you said) and 3) isn't as likely to be victim of "raids" anytime soon due to the war happening where he lives (officials seem to have obviously more important things to worry about).