Combine the milk and rice in a large saucepan. Cook, stirring, over medium-low heat until the mixture boils and thickens, about 25 minutes. Stir in 1/3 cup maple syrup and cook 10 minutes more. Add the orange rind and vanilla. Pour into 4 (8-ounce) dessert bowls or custard cups; then allow to cool at room temperature. Meanwhile, heat the walnuts in a small heavy frying pan over low heat, stirring, until fragrant, about 3 minutes. Drizzle with remaining 2 tablespoons maple syrup. Cook over medium heat, stirring, until the syrup boils and coats the walnuts, about 2 minutes. Sprinkle on the puddings.