Professor of Organ at the Geneva Conservatory until 2001, Lionel Rogg has welcomed students from all over the world. He frequently gives master-classes and is now professor of organ and improvisation at the Royal Academy of Music in London.
He has written an Improvisation Course for organists, published in French and English by Editions Musicales de la Schola Cantorum. Volume 1 is practical harmony, ornamental counterpoint and chorale. Volume 2 is modal and free style. See a complete review of volume 1 here.
Organ Improvisations on Bach Toccata & Fugue in D Minor
This recording features many performers, including Lionel Rogg, Barbara Dennetlein, Frederic Blanc, Holm Vogel, Johannes Mayr, Vincent Thevenaz, and David Franke. There is a video below that is likely made from this recording, but until I get a copy of the recording this is an unverified claim.