Heat the oven to 350°. Line two baking sheets with parchment paper or aluminum foil. If using foil, coat it with cooking spray.
In a small bowl, stir together the stuffing and the stock. Let the mixture stand for about 2 minutes to soften.
Place the turkey in a large mixing bowl. Add the salt, pepper, apple, onion, poultry seasoning, eggs, and stuffing mixture and stir until well blended. Form the mixture into 1 1/2-inch balls and put them on the prepared baking sheets. Bake until they're cooked through, firm, and golden, about 20 minutes.
While the meatballs bake, make the cranberry dip. In a medium saucepan over medium-high heat, stir together the cranberries, orange juice, and sugar. Bring the mixture to a boil, then reduce the heat to low and simmer, stirring occasionally, until the mixture is slightly thickened, about 10 minutes. Remove the pan from the heat and stir in the mustard. Use an immersion blender or food processor to puree the sauce. Serve it on the side with the meatballs.