I find large bags of tapioca every time I go to T&T, often available in both black and white (clear). Sometimes H-Mart has it too, but it doesn't seem to be as cost-effective or readily available as it is at T&T. If you have any other Asian market near where you live, check there. If they don't have it, or if you don't live near a well-stocked Asian market, buying it online is probably your best bet. Tapioca is available in small, ready-to-serve pouches, but it's usually more cost-effective to purchase it dry in large, vacuum-sealed bags and cook it yourself.