Half of the responses aren't even relevant to the original topic, only stating that they've acquired the Magnificence of Leather and Magnificence of Scales.
We're looking for Magnificent Hide Pack (36 slot bag)! I have yet to find where to obtain the pattern for this. No information is given in the patch notes, and all new recipes I've learned using Magnificence of Leather have only been gear for Shamans.
Considering the Magnificent Hide Pack requires seven(7) Magnificent Hides, I assume that it is either rare to learn, or is learned after learning all the other patterns you gain from using Magnificence of Leather/Magnificence of Scales.
It's a random discovery from Magnificence of Leather or Magnificence of Scales.