Corporate Author. (Year of Publication). Title of document: Subtitle of document. (Report No. if Provided). Place of publication: Department.
National Institute of Mental Health. (1990). Clinical training in serious mental illness (DHHS Publication No. ADM 90-1679). Washington, DC: U.S. Government Printing Office.
Note: Use Author as the publisher name when the author or issuing agency is also the publisher.
An excellent Guide to consult on citing in APA including how to cite Government Documents in APA.
A Brief Guide to Citing Canadian Government Documents and Statistics (Queen's University) has more examples.