You can make your own quite easily! It takes just two ingredients - plain or all purpose flour and baking powder. Just remember that different brands of baking powder perform differently. So it is adviseable to check the instruction on the box of baking powder you are using. In Australia to make self raising flour you will need 2 teaspoons of baking powder to each cup of plain flour. However in the United States, you will only need 1 1/4 teaspoons of baking powder per cup of  plain (all purpose) flour. In other countries, please check your brand of baking powder.