For more information see sections 3.13.2 and 3.15.5 in the AMA Manual of Style, 11th ed.
Section 3.13.2 gives some specific information to include (when available) for government/agency reports:
Author(s). Title of bulletin. Name of issuing agency; Year. Series name and number. Accessed [date]. URL
This essentially treats reports as books or chapters in books.
If the US Government Printing Office is listed as publisher, try to locate the issuing bureau, agency, or department.
Section 3.15.5 applies to electronic references specifically and suggests treating these reports journal style for articles and book style for monographs.