Watch the World Burn Achievo

[clueless]

just cant find the incinerary shotgun
been to all gun shops
searched military caches
did 6 supply drops
any other places to look?

[WillieSea]

Any loot location that has a gun case.
Sometimes in campsites, post office, houses. Any place you have seen a gun case.
If you are on breakdown, you could advance to the next level to reset all the loot locations and try again. After all, it is about RNG.

You could always mod the incendiary weapons to show up more often in the game.