Research reports are generally written and published by organizations. They might be made available by the organization on its website, or they might also sell access/printed copies to libraries.
Don't confuse these reports with research articles published in journals. Reports are more like a book, often hundreds of pages long.
There's no one best place to search for these, but there are three good options: Omni, a database, and the web (Google).
Look for these as hints that it's a report, rather than a book:
Start by searching Omni, using a keyword search. We've purchased many reports, in print and online.
If you know who wrote the report, include a word from the organization's name as a search term.
Otherwise, just search for your topic and look through the results for something that looks like a report.
It's noteworthy that Omni considers reports to be books, in most cases. There is no filter provided for reports.
The Canadian Documents Collection includes thousands of research reports from Canadian organizations. The majority of these are also listed in Omni, with direct links to the database, but you can search the database directly.
Many publications are available on the websites of the organizations that produce them.
A regular Google search could be very useful for finding these documents if they're on the web. Try searches like: