I'd always read that only about 15% as much potassium as sodium is LOST in sweat, and that's why electrolyte drinks don't have much.

SaltStick cites a lot of the research on their page: http://www.saltstick.com/products/sscaps/cpotassium.htm

Honestly, if you're getting 6-700 calories a day from fruits and vegetables as we all ought to anyway, I think that will take care of potassium needs unless you've got some other kind of imbalance going on.

Personally I can't get enough sodium or magnesium without supplementing. Potassium has never been a problem for me.