I went to nearby monster sized HEB grocery store here in Houston Texas, lots of different flour types, especially many by Bob's Red Mill brand, but no Tapioca Flour. Next tried large Eastern Mediterranean ethnic store Phoenicia, nope. Lastly tried small Pho Saigon Vietnamese grocery store where cutting up lots of large fish, and surprise, Thailand made cheese Brand Tapioca Flour, 400 gr/14 ounce for USD0.68.
Well package says Tapioca Starch or Farine de Tapioca and I'm pretty sure that Farine in french mens flour. Has same consistency as corn starch so must be it.