The 13th movie Celebi was an event a long time ago. Her is how you would get the Zorua with it.
In the lefthand building in the northern road of Castelia City heading to Route 4, you will find a man similar to Primo in Violet City and a variety of other characters throughout the history of the games, who will give you the ability to give him a phrase. This phrase, like the phrases in the past, unlocks a new feature. However, unlike Mystery Gift, this one will unlock the Relocator. The words are as follows; Everyone, Happy, Simple, Connection.
To use the Relocator, you need two DS systems, the model of which is irrelevant. The DS with Pokémon Black & White will send out a DS Download Play program over wireless. Access this over the DS Download Play option in the DS's main menu for the DS holding Diamond, Pearl, Platinum, HeartGold & SoulSilver. This will load up the system.
When you transfer Celebi over from the Generation IV games, you will be able to find two characters in one of Castelia City's buildings; the GameFreak building. When you talk to the character with Celebi in your party, Celebi will pop out of its Pokéball and Zorua will change from its Illusion. The trainer for Zorua will give you it as a gift due to how well they played together. You need a PokeBall of any variety in your bag.
So that is over, but there is another way using the event Shiny Legendary Dogs; You only need one. This event is over too, but you could possibly have them in your Gen 4 game.
When you transfer Raikou, Entei or Suicune from your games to Black & White, you will be able to get access to the Lostlorn Forest area. This area will feature a character who mentions a Pokémon that has been known to create illusions. You will find a Pokémon matching one of the beasts that you didn't transfer over. If you send over Raikou, you will see Entei. Send over Entei and you'll see Suicune and send over Suicune and you'll see Raikou. When you attack, you'll see that it is in fact a Zoroark. This is the only way you can capture Zoroark.
This will give you Zoroark, which you can breed for infinite Zorua :D EDIT: You need the Relocator here too.
Other than those, there is no way to obtain them other than hacking a Zorua, or one of the event Legendaries that you transfer over.