You will need to find Perfect Asgardian Steel if you want to craft some of the best Gear in God of War, but these resources are difficult to come by. So where do we even get Perfect Asgardian Steel?
The answer is that Perfect Asgardian Steel can drop from any Valkyrie enemy in the game. You get them randomly by killing them, but expect to kill a lot off them before you get one. You do however get an increased chance as you kill more, since there is a limited number of Valkyries that you can kill, and the game will give you all the Perfect Asgardian Steel in the game when you have killed all the Valkyries.
The best method to farming them is to just keep killing all the Valkyries you come across in the game, and you will likely get enough Perfect Asgardian Steel soon enough.