The Victory Medal was a drop from Valkyries in Aether I. They were only found in Silver Dungeons . After you have killed 10 Valkyries (which means 10 medals in total if you didn't die), you could challenge the Valkyrie Queen.
Dungeon items were not normally obtainable with some mods, such as TooManyItems. Using Single Player Commands, however, Aether dungeon items were obtainable by using the ID of the item. You could get the ID's here.