You're likely to be more succesful if you use a specialized search engine such as Statistical Universe, U.S. Business Advisor, FedStats, etc. Even the specialized search services aren't always current on whether a data product is available free from an agency's web page.
More recent information is more likely to be available at an agency website than older information.
Most government information on the internet has a print counterpart. If you have a specific title, it might help you search for it. However, there are some statistical series' that are now only available on Internet, so there is no way to search by title. If you know that in the past an agency has published the information you need, look for that agency's home page. Many agency web sites include a search engine that just searches the files available from that agency.