So far, I have found Moltres,Zapdos,(obviously Lugia),and Ho-oh I want to find out if articuno can be found in the many caves that are in the Jhoto and Kanto regions so that I can capture all the legendary birds.
The wonderful Articuno can be found deep within Seafoam Islands.
Seafoam Islands is pretty big, so look here for a video. Not very good quality, sorry - just mute your music as well. It's really annoying. xD
Hope I helped. :)
Yes in the Seafoam Islands.
Hope this helps!