This quest is not available in game.
Mehlar Dawnblade at the Bulwark wants you to bring him 20 Minion's Scourgestones.
It is time you remembered history that should not be forgotten... the slaughter of our people by Arthas and his Scourge army.
Vengeance on the Scourge is the only way to ease your pain. It is unfortunate they are not susceptible to fear and pain. Only their utter destruction will bring you even a shred of satisfaction.
Speak with Argent Officer Garush for knowledge of scourgestones and how to obtain them -- I will need to see many of them as proof of your commitment before we speak again.