There are now 191 signatories to the Stewardship Code. The most recent signatories are highlighted on this list:
http://www.fsa.go.jp/en/refer/councils/stewardship/20150611/02.pdf
The Board Director Training Institute (BDTI) is a "public interest" nonprofit in Japan dedicated to training about directorship, corporate governance, and related management techniques. It is certified by the Japanese government to conduct these activities as a regulated nonprofit. Read a summary about BDTI here, and see a menu of its services for both corporations and investors here.