The following databases can help locate research studies produced by think tanks and non-profit and privately-funded organizations.
Columbia International Affairs Online [CIAO] -- provides the full text of a wide range of scholarship books, working papers from universities and research institutes, occasional papers series from NGOs, foundation-funded research projects, and proceedings from conferences.
Policy Archive -- a growing archive of global, non-partisan public policy research. It makes use of technology to collect and disseminate summaries and full texts, videos, reports, briefs, and multimedia material of think tank, university, government, and foundation-funded policy research. It offers a subject index, an internal search engine, useful abstracts, and email notifications of newly added research studies.
PolicyFile -- provides full-text access to U.S. foreign and domestic policy papers and gray literature published by a wide variety of think tanks, research institutes, and agencies. PolicyFile is updated weekly with abstracts and links to the latest reports, papers, and documents.
Think Tank Search -- produced by the Kennedy School of Government at Harvard University, this search engine searches the websites of more than 690 institutions affiliated with universities, governments, advocacy groups, foundations, non-governmental organizations, and businesses that generate public policy research, analysis, and activity.