A-22B Chao

You can find the crafting spec in two gigs....the first is in the Guinea Pigs gig and it's in a chest close to where you find Joanne Koch, and the other one is in The Frolics of Counsilwoman Cole gig. It's on the big boat that you see during the gig, but there are several enemies looking/guarding the boat so you have to take them out or sneak passed them using optical camo. 

As for the gun itself is concerned you can buy it in the weapon shop in the eastern badlands (Not the one in the Aldecado's Camp). There is another one that you can get in the Tyger and Vulture gig in a slightly concealed chest beside Vortex's chip (The chest looks like a safe you usually see money in).