shb,
Another word for sweet rice (Oryzae glutinos) is glutinous or sticky rice.
It contains no gluten, though.
Ordinarily, you could get koji at Quality Natural Foods (
http://www.qualitynaturalfoods.com/shopnew/display.cgi ) but it looks like for the moment they are out of stock!
So go to Cold Mountain at MiyakoKoji-San and get Cold Mountain Dried Koji.
(
http://www.coldmountainmiso.com/ )
It makes very excellent amasake!
You can also often find this koji in the refridgerated section of a Japanese market.
Thank you, very much.
Bruce Paine