The robot hand can be found inside 504's warehouse once you have this area of the map unlocked. Go inside 504's warehouse and inside the blue container and you will see the robot hand is behind some cardboard boxes. The blue container is inside next to one of the doors you can enter through, in the room there will be a vcr remote and a monitor and there will be a pile of cardboard boxes where you will see the robot hand poking through from behind the boxes.