How do you get lengendary Pokemon in Vortex?

There seems to be a misunderstanding. There is no Pokemon game or version called "Vortex."

Perhaps you're thinking of a different Pokemon game or a fan-made game with that name. Could you please provide more context or clarify what you mean by "Vortex?"

Once you provide more information, I can help you figure out how to get legendary Pokemon in that specific game.