Both of the following search engines are run by the Government Printing Office (GPO) to discover government information.
Major commercial search engines such as Google can be searched easily for government publications using the "site:" search command. To do this, begin your search with site: and then the website you want to search within (no http://www and no space between the colon and the website), followed by your usual search terms.
A search of the EPA's website for information about climate change would be:
site:epa.gov climate change
A search of the Ohio Secretary of State's website for information about absentee ballots would be:
You can also search all .gov websites with a search for "site:.gov" though this will include the federal government, many state governments, and even some local governments.