How do people find potassium amounts in foods?

I was adding chocolate to my lunch and found it in the database. The nutritional info was correct, except it said each serving had 650 potassium. The food label is in front of me and potassium isn't listed, so how did this person know the chocolate has that much potassium? Is it only in U.S. and Canada that it's not listed? Is there a top secret website that lists the potassium amounts in foods?