This Japanese webshop sells them, and I have to say they look appealing. Pretty cheap. But I have never heard of the kuromaku line of Shapton before. I can find plenty about their glass series for instance, but not about this ceramic series.
If these stones are any good I might try some, as I've ordered a couple of Noren from this site and the shipping to the Netherlands was good, quick and cheap, opposed to buying stuff off the bay from the USA.