I Have An Over Active Thryroid... Take Medication To Slow

I have an over active thryroid... take medication to slow it down... all is good there. I had graves disease and eye surgery....over 15 years ago. I have been taking Potassium Iodide and ran out... now I can NOT find it on the shelves of the local stores that sell over the counter medications....vitamins etc. Where can I purchase Potassium Iodide? I found you charge for this service... so I am not paying for non medical advice.... bye.