You’ll find this magazine in south eastern Mojocoyo province, in a cartel cocaine hideout. The accessory case is upstairs in the building nearest the road.
As you can see in the video, when I approached from the road, maybe I was just lucky, but there were no cartel between me and the target building, so I was able to just walk right in and take the accessory.
This magazine is for the MP7 SMG only (available in Barvechos). It increases the standard 20 round magazine capacity by 50% to 30 rounds, which should help avoid such frequent reloads.
If you rock the MP7 in your load out, I recommend this high cap mag, and it’ll give the MP7 more of the appearance you probably recognise.