The leatherworking PVP recipes vendor is located in Shrine of the Sever Stars (Vale of Eternal Blossom), the main building. See the map.
The vendor is named Tanner Pang (a male panda), he is exchanging each recipe for one Spirit of Harmony.
This is for Alliance, for Horde there should be a NPC like this one also inside the main building from Vale of Eternal Blossom, I think is Shrine of Two Moons (I’m not a Horde player).