Sodium Chlorite can be purchased at any pool supply store. You will need very little of it. 100 grams will likely serve you for the rest of your life.
Pool supply stores tend to have sodium chlorite in white flakes that are 80% concentrated. Mixing 10 grams of these flakes with 20 ml of water will produce the concentrate of roughly 28% that is used to treat systemic illnesses like malaria, Flu or the like. Heating the water will allow it to dissolve more readily.
Once mixed, put the concentrate into a dropper bottle. 10 drops are then placed in a glass and a half of a lime is squeezed into the glass. After about 2 to 3 minutes, it will appear greenish and a notable chlorine odor will be present. It should be ingested at that point. Once you have activated it with the citric acid of the lime, it must be used soon.
Do not consume anything with vitamin C in it afterwards. This tends to reduce the effectiveness.