Bond & Faye's Supplement to de Ricci's Census, pp. 517-24
Mr Walton has sold a number of his manuscripts individually while he was alive, many of them to Sam Fogg, and an auction was held after his death: Bloomsbury Auctions, New York, 14 May 2009. They may be recognised by his purple-stamped number, often on a cutting from the catalogue in which the manuscript is described
