Find the major national associations/organizations on your topic by Advanced Google searching. Limit to Site or Domain .org
For example, an association for Alzheimer's patients and families would be: ALZ.org (Alzheimer's Assocation)
Also try limiting to .gov sites, which are great for statistics.
For example, Women's Health.gov has a fact sheet about lesbian and bisexual women, indicating health concerns/risk factors.
General Vulnerable Population Information
Racial and Ethnic Minorities