The resources below I list in addition to the obvious, which might be, of course, the search of the websites of the relevant governmental institutions and agencies, as well as the open web itself, beginning, perhaps, with the links to SPU full-text available via the SPU link to Google Scholar (but if not that, then certainly Google Advanced).
Also, 1) the databases listed under Journals & Magazines and 2) some "Book" catalogs will also have indexed many of the relevant government documents. For example, the Harvard catalog has ingested a lot of the cataloging of the relevant documents done by the Harvard databases, such that Keyword and even Subject (though not always Library of Congress Subject Heading) searches of the Harvard catalog will turn up many of those even ahead of, say, the traditionally published books, essays, and articles on the topic in question that Harvard has purchased. So the Harvard catalog would be a good example of a "Book" catalog that can be used as a way of identifying at least the titles of some of these government documents, and thus help to render a web (or govinfo) search for the full-text a bit more specific.
Help with Government Documents as given by the University of Washington Libraries:
