See here for useful advice (although you will, obviously, have to studiously ignore the higher carby foods):
"Many foods contain potassium. All meats (red meat and chicken) and fish such as salmon, cod, flounder, and sardines are good sources of potassium. Soy products and veggie burgers are also good sources of potassium.
Vegetables including broccoli, peas, lima beans, tomatoes, potatoes (especially their skins), sweet potatoes, and winter squashes are all good sources of potassium.
Fruits that contain significant sources of potassium include citrus fruits, cantaloupe, bananas, kiwi, prunes, and apricots. Dried apricots contain more potassium than fresh apricots.
Milk and yogurt, as well as nuts, are also excellent sources of potassium."
So if you're cramping, I'd try adding a few nuts as well making sure you're eating broccoli with your meat/fish.