What's the right approach to take for referencing anything that isn't preserved in an institution like the Library of Congress? Say the interview of a person,

What's the right approach to take for referencing anything that isn't preserved in an institution like the Library of Congress? Say the interview of a person, a niche publication, a local pamphlet? Maybe to certify that your article is of a certain level of credibility you need to manually preserve all the cited works yourself in an approved way.