Read biographies of Margaret Fuller and A. Powell Davies in the online Dictionary of Unitarian and Universalist Biography.
Information about Thoreau can be found in Thoreau as Spiritual Guide: A Companion to Walden for Reflection and Group Discussion, by Barry M. Andrews (Boston, Skinner House, 2003).
Thoreau as Spiritual Guide A Companion to Walden for Personal Reflection and Group Discussion
From Skinner House Books
A fresh reading of Walden as a meditative companion, teaching tool and guide to personal growth. Discussion questions included for group or personal use.