For specific types of government publications (tax forms, laws, hearings, etc.) you might want to search this LibAnswers system Try the Topic: Government Information. But if that doesn't help...
Do we own it?
Available from the federal government?
Govinfo Free access to official government publications
MetaLib A federated search engine for many government databases
USA.gov The government's own search engine for federal, state, and local websites.
Catalog of U.S. Government Publications A searchable list (rather than database) of government publications. Some links to full-text.
A non-government source with hundreds of thousands of government publications