Zoroark is a special pokemon in Pokemon Black that can’t be caught using regular methods.
You can only get Zorua if you have an event shiny Raikou, Entei, or Suicune in your party. Take your event shiny pokemon listed above to Lostlorn Forest, and you’ll see a pokemon that looks like a legendary that actually turns into Zoroark when you engage it.
Zoroark can be bred however, so there should be plenty of people on WiFi willing to trade them.