talk to the girl in sandgem town in the house directly south of the pokemon center. She will tell you a random pokemon that can be found on a random route, but only for that day. If you are lucky, she will say the pokemon you are looking for, or you can migrate an absol from a GBA pokemon game. You can also find out about swarming pokemon on the TV in any building to catch it in a swarm.
awesome thanks i''m a pokemon FREAK and i love absol and eevee plus its evolutions(: