go to iron island and search for riley there, fight together with him until you face the galatic members, after that he will give you a egg containing a riley
bonus:when the egg hatch remember the exact time and day of the week (ex. it hatch on 12:00 on friday)go there on that time and search when your lucky you might find a green globat, but remember it's not easy to see it, i got a green golbat this way, but i have gone back there like 4 times before i got it