Highlighted resources where you can search for technical reports. Try searching "technical report" + topic in the search box. For a more comprehensive list of resources, check out the Find Technical Reports guide from Dalhousie University.
"Science.gov is a gateway to U.S. government science information. The portal offers free access to research and development (R&D) results and scientific and technical information from scientific organizations across 13 federal agencies."
"WorldWideScience.org is a global science gateway comprised of national and international scientific databases and portals. WorldWideScience.org accelerates scientific discovery and progress by providing one-stop searching of databases from around the world."