If you use your library's inter-library loan program you can get a book called William James Durant: An Intellectual Biography by Raymond Frey (Edwin Mellon Press; NY 1991)... it is also called Studies in the History of Philosophy Volume 18. This is a very good book which quotes extensively from contemporary reviews of almost everything the Durant's published.
Also if you think of the Story of Civilization as a massive guide to further reading and just follow the endnotes...
