Leeds Library in England has a large collection of documents by and about d’Eon de Beaumont. At this point it is not digitized, but a catalog of the documents can be viewed.
Papers of Charles Chevalier d’ Eon de Beaumont at University of Leeds

Leeds Library in England has a large collection of documents by and about d’Eon de Beaumont. At this point it is not digitized, but a catalog of the documents can be viewed.