I don't think it drops at all. It was meant as an early boost for season pass holders. It is only level 5 anyway. There are no blueprints for it, and it doesn't drop later in the game. Oh, and in case you are asking for the SHIELD commendation regarding collecting all the named weapons and gear, it is not counted towards that.
It was clarified that it does NOT count. Go over the list again. I kept swearing I had them all but it wouldn't pop on my 3rd account. But, it turned out I was combining the Thompson and the Tommy Gun. In a previous one, I forgot about one of the pistols.
You probably have a list, but here's a good one.
https://forums.ubisoft.com/showthrea...rshal-Live-Now Look at the post #6 or so, it explicitly states that it is not required.