Industry Codes for Nonprofits
National Taxonomy of Exempted Entities (NTEE) code - used by GuideStar and National Center for Charitable Statistics
NAICS and SIC - determine the code for your industry and look at appropriate U.S.conomic Census and other reports, and in First Research (see below). If you know your National Taxonomy of Exempted Entities (NTEE) code - consult NCCS' conversion table for NAICS/SIC.
Trade Associations & Local Advocacy groups
Look for links from nonprofit organization web sites and other areas. Use Google Advanced Search to identify local organizations, limiting to nonprofit and government domains. For example, search: massachusetts homeless site:.org,.gov
Nonprofit books & statistical sites