Seems like most iodine tabs I've bought were in glass bottles with steel caps. Even then it says that they lose potency once open.

Is there a reason you want to use iodine? I'm not a scientist, but from what I've read iodine isn't all that great for water disinfection. Supposedly chlorine dioxide is the really good disinfectant. Aquamira and Potable Aqua both make chlorine dioxide tabs.

Aquamira also offers a type where one mixes two chemicals and creates the disinfectant. I assume (but haven't researched) that buying in the two chemical form is cheaper.

HJ