First, unless prescribed by your doctor, do not take it on your own. As a nutritional supplement it is not reccomended. Instead, try to get it from food.
Seaweed, any sea food, and onions are very rich in iodine.
There is also salt with iodine but I do not reccomend overdoing it because too much salt is bad for your body. Very bad even! The smallest thing that can happen is to make your body retain too much water. As for the worst things, there are too many, including increasing your blood pressure.