Cook the wild rice and brown rice in separate pots according to the package directions. Cool completely.
Mix together wild and brown rice, corn, celery, carrot, onion and cranberries in a large bowl.
Whisk together the vinegar, oil, orange rind, salt and pepper in a small bowl. Pour over the rice mixture and mix gently until evenly coated. Cover with plastic wrap and chill, about 2 hours. This may be done up to 2 days ahead, covered and refrigerated. Makes 18 servings.