The Violet Spellwing is obtained from the quest "Blood of a Titan". This quest is in turn started from an item that drops when you kill Argus (The final boss of Antorus) on heroic or higher difficulty. Every member of the raid will be able to loot the item that begins the quest unless they have completed that quest already.
This means that in order to get the Violet Spellwing, you need to kill Argus on heroic difficulty.
The item that begins the quest will be removed from the loot table at Battle for Azeroth launch! If you missed the opperturnity to get then, then there's no way to get it.