If you live in US, Jcrows is a good one. Trappers SSKI an alternative too.
UK / Europe; many; but here 15 % is similar to Lugols 5% (because they count in the Iodide contents) Ebay, health leads uk, Creedence.. many possibilities. Positive; you can get up to 100 ml. in one go, while in US only 30 ml.