Stir together 1 cup of lemon juice, 1/4 cup of honey, lemon zest, and parsley in a bowl until the honey has dissolved. Add the halved grapes, toss to coat, and set aside.
Whisk together grape juice, 3 tablespoons of honey, and 1/3 cup of lemon juice until the honey has dissolved. Whisk in the mayonnaise until smooth. Pour this dressing over the grapes, toss to coat, and serve.