I am looking for a Koji supplier (aspergillus oryzae).
Oregon Spirit Distillers
Thinking about getting your sake on Brad?
There is a Shochu maker here in Hawaii named Ken Hirata who gets his directly from Japan. He had to go through some kind of quarantine process. I would think Japan would be the place to start. Also, ask Sherman Owen. He seems to know a lot about this stuff.
Koji is readily available from several sake homebrew shops...it's googleable (is that a word?)
Also, there are several sake producers in the US and Canada that are good sources of koji...that's where I get my aspergillus. You don't need very much to get your culture going, so the amount available from a homebrew shop is reasonable. Visionbrewing.com has it, as well, though it's a little on the $$$ side. You can even get it on Amazon.com.
I used to make shochou for a distillery in Japan, and if you need help or advice on making a koji and shobu (actually, we'd say "syobou" in my Ibaraki-ben) for your fermentation, I can help with that. I'd be interested in what your proposed methodology is. I also have some experience making Korean Soju and some rice/grain hybrid whiskies.
Try GEM Cultures