Check out these well-maintained indexes of state and local home school organizations:
The Homeschool World index includes all fifty states, foreign organizations, and interest-based organizations (special education, sports, and so on).
The Homefires.com directory lists organizations in all fifty states, and notes whether they are Christian or nonsectarian in orientation.
The Homeschool.com directory lists scores of local support groups by cities and regions within states.
Homeschool Central lists both state and local groups, and maintains a separate list of national organizations.