Where does the plan for Griswold's Perfection drop?

I found multiple ingredients for this item:

http://us.battle.net/d3/en/artisan/blacksmith/recipe/griswolds-perfection

Now I would like to know where the plans can drop. Is there a specified boss / location for this or is it just random anywhere as most of the stuff in the game? Plans do tend to drop from specific bosses though.

All Legendary equipment recipes are random, but the locations of materials can be found here.

I found mine on Manglemaw at Torment V (70).

I got mine in a cache after completing bounties. Like every other legendary crafting pattern, it's 100% random (except for Reaper's Wraps). Good luck!

Its random, I got mine from a rift boss in act 1.

It looks like Act 1, Cathedral lvl 2, in the bookshelf is the place to look.