Just a Note this achievement is no longer glitched after the April 6th update
I already had 50 watches on me so I removed one and placed it on a shelf then ran to a bunker and picked up another watch and the achievement popped!
If your going for this achievement now you will find watches in container and in bunkers. To speed up you can save quit out and reload over and over pick up the watches (as they respawn when you reload)till you have 50 watches.