In Fortree City of ORAS, there is the Secret Base Guild with a base flag symbol on the front of it. What you want to do is go from there to the left all the way (you should be crossing a bridge that has an overview of the Fortree City Gym) and enter the house you see at the end. Talk to the 'Lass' girl (this is the NPC avatar name). You know it's the right house since it has an Electike inside it. For simpler steps, fly to Fortree city, go down to where you see a ladder and climb it (you should pass a Poke Mart). Then enter the house. Hope this helped!