wifi event or use an action replay although i dont think the action replay one unlocks Latios/Latias..not sure
black stone
pokelathon
Pokethan.
There is no such thing as an Ice Stone
I believe you can get a Shiny Stone in HeartGold in the Pokèathlon Prize Corner after you get 5000 Points.
Fire stone
Staryu.
By Action Replay
You can get them at the pokeatholon dome.
i think it is a leaf stone
you can find a dusk stone in the ruins of alpha
sorry no stone, they evolve by level or trade