First u go to the 6th gym bagde (city were it's located) then u go to the gym but don't go in the gym. Once ur there u go down until u see a boat then talk to the sailor and he will take u to iron island. Then go itno the cave by the house and eventualy u meet a really cool lookin guy named riley and he will follow u around until u meet some galactic goons and then after u beat them he will give u a riolu egg then walk around until it hatches and u will get a riolu
PS:if ur party is full don't worry if he dosent' give u the egg u can go and deposit a guy and come back and he will still be there