Primary sources are often found in "archives", "special collections", "exhibits", "repositories", "records", and places labelled similarly. Just remember that they are original creative works, recorded at the time of the event, and/or first-hand evidence.
Laws, treaties, regulations, census data, etc. as primary sources should be acquired from the government department or a database, not from unofficial sites.
When searching for primary sources in these databases, only use original research, case studies, statistics, lab notes, patents, etc.