Your guess is as good as mine. From the stuff I've heard and seen online, I could say that J-fans are shoddy guitarists who oftentimes can't even tell what a tab is (long story), but that'd be unfair to those few I know that are actually good. Unfortunately, aside from the sources I mention below, most tabs that I find online generally are done unskillfully.
But at the same time, Jrock tabs aren't exactly non-existent: if you have a program called Guitar Pro, you could check out mysongbook.com, where you can search by country (in this case, Japan) for Japanese bands. The software is not free, however. Also, there could be bandscores you can buy online. I've seen scores in Score.com, but since I can't read Japanese, do not know if they ship to the US. Finally, I'm sure there are programs that can let you tab out midi files of Japanese songs, of which there are plenty.