There's also red koji (aka "red yeast rice"), which is commonly used in China to make huangjiu and Shaoxing rice wine. The Japanese sometimes use it in conjunction with their usual koji to make akai sake (red sake). It's just about impossible to get red koji in the US, though, because the FDA has banned its sale as a nutritional supplement. It turns out that the monascus purpureus mold that makes red koji red produces significant amounts of a chemical that happens to be the active ingredient in prescription cholesterol control drugs. Doesn't stop people from ordering RYR pills and powder from China off the internet, but I still haven't found a source for red koji in its whole form.
The problem you're having with drying at the edges of your koji culture reminds me of the descriptions I've read for the traditional methods of producing koji by hand, which is still often used today in Japan even though there are automated methods available. I could go into deep detail, but the method really boils down to mixing the inoculated rice by hand every couple hours and keeping it balled up between mixing sessions. After reading your account of making koji, I can see why the Japanese developed their traditional method and how it would help. Keeping the culture in a ball would help keep drying to a minimum by reducing the surface area to its minimum, while spreading the rice out while mixing allows the accumulated heat generated by the mold's growth to dissipate.
It's been 24 hours now and, while it definitely 
