There is one book in the library who gives a hint of their finding spots, if it is already added in 0.8, I don't quite remember.
I also made a quest for them to make it easier to see which ones you got and give hints to the remainin ones but i do think that quest isn't in 0.8 but comes in 0.9 or 1.0 -_-
I certainly can give you a similiar hint to the one in the quest and library.
The northern plain, western plains, endless desert and frozen tundra are the areas you want to look around.
I hope this helps!