I'm not sure if there was any such topic ever made, I tried searching but couldn't find anything.
So I was looking at my Achievements -> Collectibles, checked under each category and it seems like I never managed to find anything. I'm not sure if it is a drop or you pick it up somewhere. It's just bothering me because I like to explore everything, kill more mobs than it's really needed and I'm still at zero.
I don't think it's bugged, I mean I really don't remember getting any such drop. In case I'm doing it all wrong, or if there is some other solution to it, feel free to correct me.