The Marion E. Wade Center, based in Wheaton College just outside of Chicago, IL, is the premier archive for Sayers in America, and possibly worldwide. The Wade Center specializes in the works of seven different authors: C.S. Lewis, J.R.R. Tolkien, Dorothy L. Sayers, George MacDonald, G.K. Chesterton, Owen Barfield, and Charles Williams. They have several talks you can attend if you are in the Chicago area. If you are pursuing in-depth research, contacting or visiting the archives is almost mandatory.