There are two ways you can get either pokemon. The first way is via Heart Gold or Soul Silver, by capturing Celebi and all three legendary dogs and trading them over to Pokemon Black or White. The second way is easier and cheaper. If you have a Gameboy Advance SP, get a game shark and use it to select any pokemon game like,Fire Red, Leaf Green, Ruby, Saphire, or Emerald. Select the Pokemon (Celebi and the three legendary dogs from the Johto region.) and transfer them to Pokemon Diamond or Pearl. When have accessed Palpark, get another DS and transfer them over to Black or White.
Once you've done that, you need to find Zorua and Zoroark. To find Zorua, fly or travel to Castelia city. There is a street to your right or your charecters left based on how you play (the player must be faced away from the pokemon center.) The street is next to the center. Head down that street and go into the first building on the right. In the lobby thereare two people, a boy and a girl. The girl will talk to you and the boy won't. The boy is Zorua. Have Celebi with you. To find Zoroark, fly or travel to Nimbasa city and travel to the path that goes east of the music stadium that leads out of town to one of the big bridges. There is a forest called Lostlorn Forest. Go to the very back to find a truck with a camper. Go inside to find a women that doesn't speak to you. She is zoroark. You must have the three legendary dogs of the Johto region.