Grey Literature is information that is produced outside of traditionally published means.
Grey literature is produced by government agencies, professional organizations, research centers, universities, public institutions, special interest groups, associations and societies whose goal is to disseminate current information to a wide audience. Grey literature can be challenging to track down as it is not “searchable” via traditional mechanisms.
Examples of grey literature:
Identify organizations that might be publishing this type of information on topics that you're interested in and then to search their websites. Look for website sections with names like "Documents", "Reports", and "Library". Consider government agencies, non-profits, professional associations, research institutes, and other organizations, based on the research you have already done.
Use Google site search to limit your search results to a specific website or top level domains. For example, if you want to find literature from American universities and colleges enter your search terms then site:edu. If you wan to find literature from the B.C. Government, enter your search terms then site:gov.bc.ca
Example Google search: