Calcitic limestone is pure Calcium Carbonate. If your soil is alkaline, you might experiment with reducing or eliminating the lime in this mix. These ingredients make up the bulk of the phosphorus component. I like to use bone meal. Not only is it easier to find, but also it is already being produced as a byproduct of the beef industry.
Rock phosphate is mined.
Another possible potassium source is Jersey Greensand. In addition, it does not supply micronutrients.