From what I read your best source of potassium is not in the form of a pill or a supplement. Instead it should be from fruits and veggies and raw nuts etc.
Below are some lists of veggies, fruits and nuts that contain natural potassium:
Fruits would include bananas, apples, oranges, pears, plums, apricots, mangoes, berries, melons etc. Just watch the portion size that you do not consume too much sugar in the process.
Nuts would include macadamia nuts and almonds, pistachios, cashews, Brazil nuts (CAUTION on eating more than 2 a day), Salmon and tuna fish, eggs, wheat germ, bran also contain potassium.
Veggies would include fresh tomatoes, sweet potatoes, white and red potatoes. asparagus, spinach, cabbage, beet greens, white beans and (ALL beans, except read labels and watch the salt and sugar contents of any canned beans), plain non-fat yogurt, PRUNES (watch the sugar content), carrots raw or in a smoothie, dark black strap molasses, cooked soybeans, winter or spaghetti squash, skim milk,