1-3-13 Hirakawa-cho, Chiyoda-ku; (03) 3239-8673. The store, open 10 a.m to 7 p.m., Monday to Saturday (closed on Sundays and national holidays), is on a street running parallel to Shinjuku-dori, a short walk from Kojimachi Station on the Yurakucho Line or Hanzomon Station on the Hanzomon Line.
Bonjinsha is a specialty bookstore that got its start more than 30 years ago selling preparatory materials for the JLPT, and it carries everything from specialized dictionaries for translators to educational games and toys for children. Bonjinsha’s Kojimachi shop — the only retail bookshop in Tokyo that specializes almost exclusively in Japanese-language study-and-reference materials … it is run by the Bonjinsha publisher based in Tokyo’s Chiyoda Ward that networks closely with organizations promoting the study of Japanese.
In addition to the retail shop, mail-order services are available via its Web site. It will ship to domestic addresses for a small handling fee.
Source: “The world’s best one-stop shop for Nihongo” July 22, 2009 Japan Times