An easy way to make a substitute for Five Spice Powder is to mix equal parts of anise, cinnamon, clove, fennel and Szechuan peppercorns. It is also common to include black pepper and ground ginger, so the exact recipe is best left up to taste.
Specifically, Five Spice Powder is a Chinese seasoning, and Star anise and Chinese cinnamon are used in the construction of it. However, a reasonable substitute can be made by using more common types of anise and cinnamon. In South China, Mandarin orange peel can also be used in the making of the powder. Trial and error is perhaps the best way to concoct a reasonable substitute.