I believe Sensei Matsuyama now runs the Doshi Kai Dojo in Acton, MA
Tabata is published and still very active in Shotokan Karate.
A fellow Judoka of Sensei Byrnes was Larry Garron (Former Football Player for the original "Boston Patriots"

took the Bushido Kai name to Framingham, MA where it has since changed hands.
I'm not quite sure that Tabata was Nagao's direct instructor.
Tabata is the east coast equal to Fumio Demura (Karate Kid) both paying allegiance to Obata...
Bushido Kai was the original conduit for the names you mentioned.