SuperSearch can also be used to find primary sources.
Put your search terms in and, on the results page, use the filters to select content types like video, magazine articles, and government documents:
If your research is about a specific time period, scroll down to filter by time, too:
For example, the Essex County (Mass.) court records and probate records are all available and text searchable on the Internet Archive. Look at the citations in secondary literature to determine what words you need to use to search, like "quarterly courts" for Essex Co. or "New Amsterdam" for New York.