The publication manual provides guidelines for citing reports and gray literature in section 10.4.
The format is essentially the same. The author may be a group, task force, government agency, or other organization. The publisher may be a professional organization or government agency.
The guide from Northern Michigan University linked below provides comprehensive examples and instructions, but the manual is still the definitive source.
Author's Last Name, Author's Initials. (Year). Title of work (Report No. 123). Publisher.
Name of Agency. (Date). Title of work (Report No. 123). Publisher. http://www.address.gov
United States Department of Commerce. (2015, October 2). A snapshot of monthly manufacturing statistics in the United States (MFG15-M3). United States Census Bureau. http://www.census.gov/content/dam/Census/library/publications/2015/econ/mfg15-m3.pdf