Hmmm... I don't know if GEM will do it or not, but it couldn't hurt to ask them. They do ship to several countries.
Failing that, there is a service which will export to (almost) any country Japanese products from Japan. At a cost of course, but well worth it if there is no other option.
http://www.japanonly.com/en/ Besides, once you have koji, you can use it to create more spores - Katz Art of Fermentation book I think covers this. In theory, you only need to import it once.
When summer comes around and you use some corn (that's corn in the american sense of the word, not corn as in grain like they say in Europe), please let us know how it turns out.
One totally out there option, not something I've done, but something my friend does when he needs specific mold cultures. Buy some unpasteurized stuff (in you case miso) and leave it out on the counter with a cloth over it (not air tight). After a few days/weeks, mold should start growing on the surface, and when it changes colour (ie fruiting bodies - yellow, green and/or blue for koji I think), he scrapes it off and mixes it in with what he wants moldy (in your case, steamed rice) cultures it to get more spores, and so on until he has enough spores to make what he wants.
Doing my best to be the change I want to see in the world, one meal at a time.
http://wholewheatfsm.blogspot.ca
Currently Culturing
Kombucha, perry, cider, wine (red and white), mead(s), miso, sourdough, & seasonal veg my garden gives me