The following websites have lists of shamisen instructors:
Chords Canada - lists for US, Canada, and Australia
Bachido - for tsugaru style shamisen only
If you are interested in learning jiuta or another style in particular, make sure you discuss that with the potential instructor beforehand.
When you do find an instructor to work with, always be sure to pay on time, be early to lessons, and thank the instructor after every session. Do your best to practice regularly and be honest when you are having difficulties.