I wanna give you a strategy after finding them "not sure if somebody said that here"
after seeing Latios or the other do something like this:
everytime you change the rout/city latios's location will change so
1- go to Mauville City
2- then turn left to Rout 117
3- see if Latios where you are if its not back to the city then back to rout 117 keep doing this until its on rout 117
4- make sure that you have a strong pokemon highest than lv40 has something to make latios asleep
5- make him asleep then hit him until he's red
6- throw 3 to 4 Ultra balls before he wake up and I think you will catch him
p.s u can the city/rout thing every where you want I just said Mauville/rout 177 because I did it there "twice"
This wont work because making it sleep wont stop it from fledding
It will appear randomly in the wild, because it changes it's place every time you go into a route or a city.
So its a bit hard
ya, just run around in some grass.....