Potassium is in a lot of foods. I know this very well because I spend many years on dialysis due to kidney failure and had to do a lot of diet tracking so I didn't consume too much potassium or phosphorus because the kidneys are important in removing excess amounts. Most meats, vegetables and fruits, nuts legumes all have potassium of a varying amount.

Also the USDA maintains a database of complete nutrition of many common foods.

https://fdc.nal.usda.gov/