On ebay you can purchase Potassium Iodide and Elemental Iodine in bulk or from a chemical supply house.
See portions below depending on what strength you want. I make the 15% so I don't have to deal with lots of drops.
"To make the original version, we use what amounts to a 3% (2.91%) formula (iodine and Iodine compound). The formula is simple: 80 gm. of potassium iodine (KI) is added to 4,000 ml of distilled water (roughly 4,000 gm). After fully dissolving, 40 gm. of iodine crystal is added. After the iodine crystal fully dissolves (which takes several hours), the product is packaged and stored.
To make the newer 7% Lugol's version, using the same 4,000 ml. of distilled water, the amounts of iodine use are 200 gm. of KI, and 100 gm. of iodine crystal. For 15% Lugol's, to 4,000 ml. of distilled water we dissolve 480 gm. of KI and 240 gm. of iodine crystal.
Lugol's Iodine has an optimal shelf-life of approximately one year. Many web sites encourage you to "stock up," which does not take into account this fact. You should purchase just what you need, and annually rotate out older product."