Technical reports can be institutional, national or international and they are difficult to find as there is no one stop that you can search for all. However, one can always try to search for "technical report" and the publishing body from different search engine. Here are listed some popular ones.
Publication coverage: 1972 - present
CiteSeer
Captures full-text computer science articles, papers, and technical reports freely available on the Web. Search the full-text documents or their citations.
Computing Research Repository
Computer Science Technical Reports
From the New Zealand Digital Library, this collection provides an index to computer science technical reports that we have downloaded from selected sites on the Internet. The reports are mostly in English, but there are some in a variety of different languages. The collection contains many large documents such as PhD theses. Every single word on every page of every report is indexed.
HP Technical Reports
Available here are the abstracts and full texts of HP Labs Technical Reports. Where only the abstract appears, the full text is unavailable due to copyright considerations.
IBM Research Reports
Microsoft Research Technical Reports NASA Technical Reports Server
Over 500,000 aerospace-related citations, over 200,000 full-text online documents, and over 500,000 images and videos are available.
National Technical Information Service - NTIS
serves as the largest central resource for government-funded scientific, technical, engineering, and business related information available today.
Purdue School of Electrical & Computer Engineering
US Science.gov
Science.gov searches over 45 databases and over 2000 selected websites from 14 federal agencies, offering 200 million pages of authoritative U.S. government science information including research and development results.
Virtual Technical Reports Center - University of Maryland
The Institutions listed here provide either full-text reports, or searchable extended abstracts of their technical reports on the World Wide Web. This site contains links to technical reports, preprints, reprints, dissertations, theses, and research reports of all kinds. Excellent source!
WorldWideScience.org
global science gateway searches national and international scientific databases, providing one-stop searching of global science sources. It currently searches 15 countries technical reports collections at once.
