I'd surmise that if it's really cheap stuff coming from China, that it's infringing on the patents here, but they don't care because there's no way to get to them, and they aren't actually importing it, you are. In effect, they aren't really selling it here. This is semantically a little different situation than Eshine sending Riccardo clay here (which he doesn't).
I saw some crazy cheap 3M-marked clay, coming from Hong Kong for $1.39 shipping. I can only presume it's made by/for 3M for the non-US and non-Japanese markets (since the patents are in effect there), and being illegally sold here. I'm sure it's fine clay, I'm just not sure who is responsible for infringing the patent in this case, you or the Hong Kong seller, but for less than $6 it would seem worth a try.
Disclaimer: I won't be buying any illegal ebay clay for a number of reasons (including that I have tons of clay already), and I'm not encouraging anyone else to, either. Wait until next year when the patents expire and you'll see clay pricing come down here in the US.