you cant sorry :(
Once you have the National PokeDex, Steven will tell you that Latias is roaming Kanto. Now you just have to find it.
Latias is #380 in the national pokedex, and it is a Dragon-Psychic type Pokemon.
you need to run into it in the wild on a hunch.
You can't.
Latias is number 196 in the Hoenn Pokédex and 380 on the national.
you need a cheat for it.
use an action replay
The only way you can tell latias is in the area your in is if you seen it before and you use the pokedex to search latias.
You should watch this. You need to be on the exact patch of grass, though. http://www.youtube.com/watch?v=VcJvFli71Ewyou cant without cheatz or hacks
super hustle great latios(must have latios in pokedex) great battle overwhelming latias(must have latias in pokedex) cool latios
Without seeing cresselia, you must go to bed during the night (approxiamately 10pm) and he will appear in a dream. that is how you get him on your pokedex.
you will get it in sapphire. it can appear in wild grass if you are lucky.