How does one find "suitable referees" for publishing a paper in journal? In many journals, authors who have never published anything before are required to have two or more "referees" in order for the paper to be reviewed. Who are these referees, and how can one "find suitable ones"?

Also, how does one go about finding referees when one is not in academia (i.e. doing research as a hobby rather than a profession)?
From my experience, most journals do not require you to propose referees. It's more like the journal allows you to propose some names of potential referees. The referees are appointed by the editor and you as author will not know their names.

So the answer to "How does one go about finding referees when one is not in academia?" is

You don't have to.

just find a suitable journal that does not require that you suggest referees.

If you the journal system does not allow you to submit your paper without suggesting referees, either suggest authors that you cite or authors that cite the same papers you cite (using, e.g., Google scholar).