NAICS and SIC - determine the code for your industry and look at appropriate Economic Census and other reports. If you know the 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:
See also Nonprofit Organizations Research Guide for more nonprofit benchmarking information.