Champion's Mail Pauldrons

The Champion's Mail Pauldrons are the mail shoulderguards of the Horde PvP-Rare Shaman set called the Champion's Stormcaller.

Source
This item can be purchased from First Sergeant Hola'mahi located in the Hall of Legends in Orgrimmar. It costs 4125 Honor Points and 20 Arathi Basin Marks of Honor.