All of the formulations of Surround WP that are used for crop protection, are patented. It is very unlikely that anyone licensed to manufacture those would offer anything but volume discounts.
I don't know of widespread use of the product in the SE.
During years with normal rainfall of about 50 inches, it may not be economical to use it, as it has to be reapplied after each rain event.
There are, as you noted, many locations in the south, where the white clay is extracted, usually by surface mining.
I have purchased it in powder form and in a slurry (slip) for ceramic & porcelain molding. There are many other uses, including medicinal, Kaopectate (kaolin+pectin), being the most recognizable one.
If SurroundWP were available locally(it isn't listed by my supplier), I would hesitate to use it without the advice of the State Dept. of Agriculture.
Rb