first, you need to defeat the elite 4, then go home and watch TV. it should say about a rare pokémon, then you select either red or blue (i suggest red) to get the corresponding Pokémon :)
You can find Latias and latios anywhere in Hoenn. You just have to get lucky.
in lilycove
Here is the easiest way to find latios and latias in emerald: If you have a ruby and sapphire game with latias and latios in it trade them to emerald then use the pokedex to track it down, if you don't have those games you can do what i did and go to mauville city and go to the route on your left and stay in the grass until you know for sure there not there, then go to the route to the right of mauville city and keep going back forth until you find latios and latias, now you need a wobuffet (or anything with arena trap or shadow tag) out first in your party and when you do find latias or latios weaken it until its at red hp now use loads of ultra balls to get it.. Or use the masterball as soon as you find one of them but you WILL have to get one of them the hard way unless you win the lottery in the lilycove dept store, when you get the grand prize its a masterball then you can use that on the other lati you didn't get.
You can fish a staryu in lilycove city.
latias is in the safari zone you just need a poke a ball to catch it youll find him with a mater of seconds. if you catch latias it will automatically be level 89 ,wicked or what helped me get through elite four .
Your Home
Lilycove city, while fishing with a super rod.
You purchase it in the Lilycove Department store for Y5500.
I'm shore you can
I found him over in that area thats raining.
You can only get latias in sapphire get latios from ruby or emerald.
there is no specific place to find latias but after you battle the elite four latias or latios can appear randomly and you can keep track of its area through the pokedex