If you are interested in pursuing esoteric Buddhist studies with a qualified instructor in the United States there are a very small number of Tendai and Shingon teachers in this country who take on students; there are a larger number of teachers of Tibetan esoteric Buddhism. The traditions are related, but the Japanese stream branched off a bit earlier in the history of tantrism and has some notable differences from the Tibetan branch.

FWIW, there is a broad consensus that the Kuji-in and related practices are basically a Taoist/Shugendo system; certainly the system uses elements found in the Buddhist tradition, but if you want to find someone to teach you "authentic" Kuji-in or Kuji-kiri practice, your best bet is one of the Shugendo sects in Japan.

Best,

FL