Greensand is a good source of potassium but only if you are recycling your soil since it is VERY slow release...which is also why it's so good.
Phosphorous - bone meal, fish bone meal, shrimp meal (also provides chitin!), soft rock phosphate.
Banana peel tea - banana peels and/or part of a banana boiled in water, then cool, strain and water with it.
You should read about worm composting too. The quality of your compost is really quite key to healthy soil and plants and you can feed your worms your rock dusts, greensand, kelp, etc and get all the useful benefits for the soil AND healthy microbial activity.