Urine, crushed coral, Bone meal, rock phosphate, Manure, Guano, to name a few. Good luck!
I started a Worm bin, and I find it cool because you can add things like Bananas for Phosphorus. Its like a way to customize your N-P-K, only organic!
I like a worm bin over a compost heap because it is faster especially for things like banana peels. Red Worms on average will eat there body weight in 24 hours! 1lbs of worms makes 1lbs of castings a DAY! that's a lot of Tea
Guano is one of the better sources. I used to also be able to source ( when I lived in new Zealand)a product called bio-phos was excellent stuff if you can find something similar I would highly recommend it.
"Potassium's chemical symbol comes from the Latin word kalium (alkali). This obviously makes sense because on the periodic table of chemical elements, Potassium is an alkali metal, one of 7 in Group 1"