Hi Amy, and welcome!
If you're interested in pursuing "Jonin" as a ninja leader, you might want to look for more about Maasaki Hatsumi (once known as Yoshiaki Hatsumi). He can trace his lineage back to historic ninja leaders, and has kept the practice alive. The ninja were (and to a lesser degree still are) a closed society, so be prepared to sidestep a roadblock or two.
You might also enjoy a search for the following terms:
Mikkyo
Shugendo
Kuji-in
Kuji-kiri
Happy hunting,
Bob