Cooked spinach and raw or cooked tomatoes are high in potassium, while low in carbs.
Note that potassium and sodium act yin/yang with each other. To lower potassium levels, or balance them out, consume good quality salt. This would be salt that is unrefined (still has all the minerals in it) and take a 1/4 to 1/2 teaspoon in warm water a few times per week. Then follow with ample clean room temp water to flush yourself. Good salt is great for you and if you have adrenal and/or thyroid issues, you can tend to be very low in sodium.