Here are just a few from a site I found.
I also believe an avocado has potassium in it.
Food amount in MG.
Spinach, raw 3 oz. 403
Pork, cooked 3 oz. 334
Beef, lean 3 oz. 317
Artichoke 1 bud 300
Cauliflower 1 cup 295
Lettuce 1/4 264
Tomato 1 small 244
Chicken 3 oz 242