Try searching your local pet store in the fish section. You wont be disappointed
Yeah you will. Just about everything on the shelves was either formulated by me, or was "beta" tested by me. I'll spare you the technical explanations of why, but everything commercially available is very weak, or in a chelated form. Playing with halogens in fish tanks (actually reef tanks) is considered very advanced (thin margin of error, requiring constant monitoring), and therefore the supplements are not only weak, but phenomenally expensive. In the non-chelated iodine supplements, the most commonly avail is a 1% KI solution.
You may be able to find lugols in 1/2-1oz bottles. Lugols is something like 10% KI, 5% I2 +h2o. I also pioneered (along with another biochemist) the lugols thing in reeftanks. Because a 1/2-1oz bottle lasts the average aquarist a year or two, the price is fairly high (up to $15). It's usually only carried by very advanced stores, or via mailorder from the advanced outfits. I can't name brands, but one of them is just Humco pharm lugols purchased from a local pharmacy by the case of 1liter bottles. (how do I know? I'm the one that used to buy the cases for one of the companies I worked for and did the repackaging- and they still use the same pharmacy). It can be ordered from the pharmacy- a liter costs about the same as the 1/2-1oz dropper bottles. I never extracted the I2, but it should be pretty easy, and should give a higher yield than the 7% solution. KI or NaI could easily be purchased in bulk from a chem company inexpensively (it's for your reef aquarium). I don't think they've clamped down on KI or NaI.
There are a few useful chems used in aquaria, but they are very expensive (bloodsucking companies capitalizing on peoples ignorance), and usually weak/watered down and often don't list ingredients so they can be marketed as magic-stuff-in-a-bottle. I finally got sick of it and started formulating my own supplements out of acs/usp grade chems in known amnts printed on the label, or I sold the chemicals individually for a fraction of what the shit at the stores cost. I guess I'll never get rich, I have a problem assfucking the ignorant for a profit 
(there's a very popular "magic-stuff-in-a-bottle" that's sold with a ton of extreme claims for a $25/16oz or $175/gallon.... it's simply water and sugar)
(retired)
She Who Dances With Hampsters
