This was my thought exactly - Find out where the candy otakus and/or japanophiles hang out, and test buying advertisement there, in whatever form is available/can be negotiated. This might look like banner ads, blog sponsorship, etc. Test and measure what converts to subscriptions, and renew with the ones that work.

This can definitely work with other Japanese goods. I tried a similar service (after seeing Bemmu's early success) with tea (http://teapeat.com).

With only posting to HN, I had a decent amount of sign ups.