I've been referin' to ya as Jordan for the past week, yet the one message ya actually see I call ya by your username. 'Karp damnit...
How are you going to get a Leafeon? You can only get to Moss Rock post-game.
Same way I'll get Glaceon: trade it out to evolve it. That's the only way, so it's within the rules.
... I just realized what a sinister dick move Trollfreak made. They had Eevee in the wild early on, made it's learnset more viable for in-game as well, but make Glaceon 'n Leafeon unobtainable 'till post-story. Glaceon fans like myself are not amused.