Ralts fainted, I saved can I catch it somewhere again?

[Torkoal Stu]

Title says it all dudes, is there anywhere?

 

[chosen_one386]

Later on in the game, you will meet a dude named Miror B. He will be holding any Shadow Pokemon you failed to capture.

 

[DarkerShining]

Yup, wait for the Miror B radar to go off and then you can get Ralts. That's how I got Mawile... When the radar goes off, Miror B can be at any of the pokespots or in a colosseum.

 

[Angeling]

If you saved right before battling the guy with Ralts, and after snagging any shadow Pokémon, you could have restarted..

 

[Shiny Heracross]

Not every Shadow Pokemon is re-obtainable through Miror B. Just to let you know, here are the Pokemon you can re-obtain if you missed them before simply by battling the trainer who owned them again:

Ledyba
Poochyena
Houndour
Baltoy
Spheal
Mareep
Gulpin
Seedot
Togepi
Lugia
Articuno
Zapdos
Moltres
Tauros
Rhydon
Exeggutor