I got the best potassium source youre ever going to see - Blackstrap molasses.. it has about 580mg in a tablespoon.. plus its chock full of other minerals.
It tastes like a burnt tarry licorice.. If you love licorice then youll love it.. Im not particulary fond of the taste so ive recently found out that i can mix a tbsp of it with some apple cider vinegar in a glass of water and it tastes very good... so I try to drink that concoction a couple times a day.. if calories arent an issue for you then dried fruits like raisins are an excellent choice