tapicoa flour ?
We have a recipe that calls for tapioca flour, but can't find it. If we grind the instant Tapioca would it work to thicken pies?
Yes, or even use it as is, my mom did that all the time - for 2-crust pies, don't use it as is for lattice-topped pies because the little pieces on top will remain crunchy. Tapioca flour itself is commonly available in Asian markets, usually near the grains like millet and so forth in my experience.
Asian and health food markets will carry it.
Might find it as "tapioca starch".
Yes, grinding instant tapioca would give you the same results.
You could also thicken with cornstarch.
Are you sure you're looking in the right place in the market? Every supermarket in town carries Bob' Red Mill Tapioca flour, either in the baking aisle or with the health food.