Your right, its in the swamp somewhere
latias is in Pokemon ranger signs.
If You Are A Girl, after beating latias u will received its sign
then its not latias its latios
in southern island there was latias and latios you will meet latias in Pokemon sapphire and latios in Pokemon ruby
The Latias sign looks like a sign. But you cannot register it until you have visited all the islands.
Latias' sign looks exactly like Latios' sign except upside down.
the first one is raikou the second id enti the third is suicune and the forth is latias/latios
After you beat the game and complete Rand's mission,(which is to bring him the 4th forbidden song),go to Tilikule monument.There you will meet a person from the past.He will tell you to after Latias on Latios.In the sky you will encounter Latias.
usually on thursdays from tilt village call supercharged latias/latios.honchkrow will appear in front of you he is quite fast so you will need to boost latios/latias (touch latios/latias while flying to boost).
With Latios or Latias depends on which gender you are in the game.
Latias can be found roaming the Hoenn region after the defeat of the Pokemon League. Latias's counterpart Latios can be found on the Southern Island.
From Serebii.net it seems Latias is wild in Hoenn after beating the Elite Four, and Latios can be found on Southern Island