Hey
Did a search on forums and found no thread or post about this.
I've just done the A Key to the North campaign mission and north Kyrat is now available. I understood this should have unlocked a few weapons, among them SPAS-12, but I have not seen it at all in the trading post. I still haven't finished a fair amount of side-missions and outposts in the south because I wanted that shotgun first. Also, if there is any importance to it, I did the Willis missions before the "kill Noore" & Key to the North missions.