How do you get Latios in Pokemon Ruby?

Answer 1

You Have to just keep searching random areas of the hoen region until you find him.
Ruby- Latios.

Sapphire- Latias.

Emerald- Either Latias or Latios. Just beat the Elite Four then you'll end up home after the credits. Then your mom will show you something on TV. After all what they say on TV ,say red for Latias and blue for Latios.

Answer

In Pokemon Ruby, only Latios can be found roaming Hoenn after you defeat the Elite Four. Latias can be captured, but this can only be done if you have the Eon ticket - an item given out at Nintendo Events. As vaguely said above, the only time you may encounter Latios is after you have defeated the Elite Four. After you have watched the special broadcast on TV, Latios will begin to roam around Hoenn. This Pokemon can be found in every grassy area and over water, but can never be found in caves. As soon as you walk into a building, a new Route or Fly to another town, Latios will change his position on the map. Although he generally moves to the Route directly next to his former position, Latios will move to the opposite end of Hoenn if you use Fly to reach him.

Conversely, it is Latias who is unlocked after you defeat the Elite Four in Pokemon Sapphire. This Pokemon travels around Hoenn excatly like Latios, being found in the grass and over water. Latias is equally hard to encounter and moves whenever you change your location in the slightest. Of course, like in Ruby, the respective eon Pokemon can be found on Southern Island, only available to the player if they have the Eon Ticket.

In both versions, the Eon Ticket allows you a one-time access to Southern Island where either Latias (in Ruby) and Latios (in Sapphire) can be encountered and captured. This particular Pokemon will be holding a Soul Dew and may be on a slightly higher level than the eon Pokemon you encountered in the wild.

after you beat the elite four and get the nat. dex, they will appear randomly in the wild grass
First, you need to beat the Elite Four. After that, you could find Latios anywhere in the wild. I'm sorry I couldn't give you an exact location, but there is no exact location where you can find Latios.
i found mine on my way to slateport from pacifidlog town but it may have been a glitch
after you have completed the Pokemon league talk with the tv then they wil tel you i hope that wus help ful