do you speak japanese? that'd help to talk to guys about what the local market looks like.

brotures offered fyxation bikes for a while, as a cheaper option.
check out y's road in shinjuku or shibuya. there's potential for fixed gears at those locations; other locations cater to different niches.

i got my bike off craigslist off an expat so i avoided the whole japanese and retail parts. which i came to learn later as i had to fixed up my bike to my liking.