Hey there,
just wanted to share an interesting post with you that I found on diablo.incgamers.com.
It's here: Diablo 3 Legendary Drop Rates Revealed | Diablo: IncGamers
They claim to have revealed the drop rates of all the individual legendary items.
Here are the links to the tables: (you can also find the links on the page posted above)
Drop Rates on Normal - Master difficulty
Drop Rates on Torment difficulty
There is another table which tells you which pieces can or cannot drop on certain classes (because of smart loot) but you can get that information from the other tables too (it just says 0% there if an item can't drop for that class).
Edit: Figures are accurate for Smart Drops. About 15% of all drops are not smart, and those items can be of any type, including legendaries not usable by your class.