Sharon (I think that's her name) sells it. The blue skinned elf in the top right of the map.
It also drops fairly often in behemoth.
"There once was a boy who dreamed of being a hero. Who believed sincerely in the battle to banish darkness from a world of light... but light and darkness are equal... and where one exists so too must the other... and when the boy finally realized this he had taken the first step toward being a true hero."