I've not seen it myself, but a book was published last year (billingual) with reviews and maps of vegan restaurants in Kanto and Kansai

"Children of the Carrot"
http://www.childrenofthecarrot.info/index.html

If you buy it, check this page: http://www.childrenofthecarrot.info/updates.html for updates.

They're also hoping for any leads: http://www.childrenofthecarrot.info/volunteer.html