HNaO3S or Sodium Bisulfite is used in wine making. You can get it at a brew store. $.75 per 2 0z. It will be labeled as sodium metabisulfite(Na2S2O5). For what you are doing there is no difference. If you buy it off the web from a chem store you will pay more because they only sell tech grade and reagent grade. Both a much purity then you will need.
Other uses are: As a disinfectant and bleach, particulary for wool; in dyeing for preparing hot and cold indigo vats, paper making, a stripper in laundering. But most important for your use it is an anti-oxidant and perservative .. Shelf life, 1 year, store in cool place in a SEALED container. "The Merck Index, Eleventh Edition PG. 1358"
I use it for cureing eggs but I can't tell you the formula, Sorry.
You can also get Sodium Sulfite from a photo store. Very similiar but not the same. If you need more information let me know.

MJ