Very possible. Using this program, PokeGen, you can get any pokemon with any move, ability, items, etc. I used this program to get all my Pokemon.
They have a check box named "Fateful Encounter". If you checked, it will be treated like an Event Pokemon in the game.
Shaymin turns into Sky Form when exposed to Gracidea Flowers. A woman in Lacunosa City Pokemon Center will give you them if you show her a Fateful Encounter Shaymin. I checked the box for my Shaymin and showed her, and i got the flowers.