That is the real trick then.  I would suggest that you consider perhaps even artists who may not necessarily be in Japan, but do work that would appeal to the manga reading community.  If you are a purist and think that such artwork simply must come from Japan or it isn't real, I would suggest that you are buying into a myth and would be willing to pay the "tax" that comes from getting stuff like this from conventional channels.

I'm not familiar with the manga publishing industry, but it seems from the description here that it is similar in nature to the RIAA and ASCAP in terms of how they squish down aspiring artists and really only exist to support the established artists.

The technical side of things isn't really so much of a problem (especially on this forum), but recruiting those who might contribute the artwork would seem to me as a significant challenge.  It would seem that you might be able to find some through social networks like Facebook or Twitter, but you should try and also see if you can figure out the sites that are typical in Japan too, or at least in Asia.  I would especially recommend South Korea as a potential recruiting area as they are very well wired to the internet, have some really amazing cartoonists/animators, and wouldn't mind "sticking it" to Japan on something like this too.

Getting customers isn't nearly so difficult, as the manga reading community is quite a bit larger and many of them speak English as a primary langauge (at least sufficient to make this a profitable enterprise).