The achievement is currently bugged! The only way to get it is if either the Host secures it or you are the Host, in case a client secures it. If a client secures it, only the host receives the achievement.
EDIT: Apparently that's been fixed with one of the patches.
EDIT2: Was apprently still broken and has been fixed again with patch 1.3.1.

The item is a RNG drop which means that there is only a percentage of it to even be collectible. Guessed by the amount of tries it took me, I'd say the drop-chance is about 10%.

The achievement will unlock once you throw the hand into Caleb's truck and secure it.

The hand will spawn right in front of the Lincoln statue, right after Caleb blew up the wall. The Lincoln statue is almost at the end of the mission right besides the blown up wall.