The Aura Pass is an item introduced in Generation IV (Diamond, Pearl, and Platinum) and later games. It is used to access the Distortion World, a special location in the game.
FireRed is a remake of the original Red and Blue games from Generation I. It does not include any items or locations from later generations, including the Aura Pass or the Distortion World.
Therefore, you cannot get an Aura Pass in FireRed, and it's not even a relevant item for the game.