Academic conferences often produce published proceedings, which are a selection of papers presented at the conference.
Reports are often written by companies or government organizations. Here are some sources to check out:
Universities and research centers may make the working papers of their faculty available prior to publication.
Masters' theses and doctoral dissertations may be requested through interlibrary loan. Use Dissertation Abstracts Online to identify theses and dissertations to request.
'Grey Literature' refers to material that is not published commercially, such as reports, theses and dissertations, conference proceedings, annual reviews (a collection of chapters written by different authors on a specific topic), and working papers (research in progress).