You can in Mystery Dungeon Blue and Red. You can get Articuno in Time and Darkness too, if you use wonder mail. From N.S.
ho-oh lugia dialga palkia raquaza manaphy jirachi groudon kyogre and mew two and mew
Stratos lookout
At Sky Stairs Summit through a nintendo event
It is raquaza and it is really hard to make it join
THERE ISN'T A WONDER MAIL CODE 4 THAT
Wishcash after you beat raquaza and a bit further in the story
Raquaza (sorry if I mispeled that)
that's it i think
To get Stratos lookout you have to recruit raquaza. It will come with it. Same withgroudon and koyogre.
Teach a Pokemon fly then go to Raquaza then use the move fly on him.Also have a friend bow to recruit him.
raquaza is a master legendary Pokemon in emerald ruby and Sapphire. his is most likely to be the best Pokemon in the series (Case in point)
To get the hm dive you have to beat raquaza and and see the credits then you go to wiscash pond and wiscash will give it to you.