Where do you get Aphelion Dustwake

Go back to the Battlefields of Atria( AFTER YOU DIE THERE). Go to where you died, on the bridge area. Continue going foreward. Then there will be a save flower. SAVE!!
Continue up and you will go through a cutscene and you will have to fight Wiseman And the Black Dragon. You will get Aphelion Dustwake after killing Wiseman.