Research reports are generally written and published by organizations. They might be made freely available by the organization on its website, or they might sell print copies (or access to online versions) to libraries.
Policy documents are normally published by government organizations or affiliates. They are also normally freely available on the open web.
Don't confuse reports and documents with research articles published in journals. Reports are more like a book, often hundreds of pages long.
There's no single best place to search for these, but there are three good options: Omni, a database, and the web (Google).
In Omni, it's not always easy to determine what's a report or document, because Omni tends to consider them all books. There is no filter for reports.
Look for these as hints that it's a report or policy document:
The Canadian Documents Collection includes thousands of research reports from Canadian organizations. The majority of these are also listed in the Library Catalogue, with direct links to the database, but you can search the database directly.
These are some examples of reports you can find in Omni. Many more are available.
To find them, use a keyword search for your topic, then look through the results; they're not identified as reports in Omni, so you can't limit to reports. Use the criteria above to recognize reports.
Many organizations provide access to their research reports via their website.