You get a Togepi as an egg once you defeat Team Galactic and you go to where the Poke Mart is in Eterna City.
You get an Eevee from a girl called Bebe who lives in the house next to the Pokemon Center in Hearthome City.It is at Lv 20.
You get a Porygon at Lv 25 by talking to someone in one of the houses behind the Pokemon Center in Veilstone City.
You get a Riolu as an egg by helping someone called Riley defeat the Galactic Grunts on Iron Island.