I can personally vouch for GLSEN to some extent. I've interviewed GLSEN staffers twice for stories, though not about the particular issues of teachers facing legal requirements to out queer students to non-supportive parents.

They have a wealth of resources available for teachers, from legal reading material to networking lists by region, state, and even major metropolitan area. They have decades of experience supporting queer students and queer/allied teachers.

A really dedicated, knowledgeable group of people!