You might try searching academic and research databases such as Google Scholar, JSTOR, or ScienceDirect for published articles, papers, and scholarly works on the subject of mentoring theory. Some possible search terms to use might include "mentoring theory", "models of mentoring", "theoretical foundations of mentoring", or "mentoring frameworks". Additionally, you could explore books on mentoring and coaching to survey the range of theories, models, and approaches being used in the field. You might also try contacting mentoring experts or practitioners for their perspective on the latest developments and trends in mentoring theory.