User blog comment:ArceusFan2013/January 6th - After a LOOOOONG break,/@comment-24190135-20140106132703/@comment-24190135-20140106144952

Actually there are Articuno, Zapdos and Moltres. To found them you have to:

A: Complete the game (beat Cintia)

B: Have the national pokedex

C: Go to Eterna City

D: Go to the last house, in the souwest part of the city.

E: Talk with Oak. He says that three pokemon are across Sinnoh, so use the MapMark function in your poke watch to find them.