Can't learn recipe for Burnished Essence which makes it so you can't unlock certain Tmogs

As the title says, it seems you can no longer learn the recipe for burnished essence from Draenor leathercrafting which means there is no way to unlock old Tmogs like the golden supple helm.

I just ran into this problem too while collecting old recipes. The garrison vendor still sells the recipe, but when I try to learn it, I get the message, “The spell is not available to you.”