Hi Zoebess,
Since the SUPERTONIC is made with vinegar, it has already fermented as far as it can ever possibly ferment and so it's NOT as critical as far as storage goes as compared to a tincture. I store the SUPERTONIC, that I've made in past classes, in both clear and amber containers in a cool dark place (kitchen cabinet).
I've found FRESH Horseradish Root in shallow baskets in the produce section of a few grocery stores, but mostly in a food coop or a health food store. You can also find chinese daikon (horseradish) or japanese wasabi (horseradish) in oriental grocery stores.