The Erotica Bibliophile is an ongoing research project on vintage erotica published during the 19th and early 20th centuries, including: the history of erotic literature, a collection of the erotic illustrations and drawings, and information on the publishers and artists.
Many of the important erotica illustrators active during that period are represented here through their drawings as well as many detailed check-lists of publications that contain that artist's work; artists which include: Martin van Maele, Felicien Rops, Luc Lafnet, Louis Maltese, Paul Avril, etc.
If it's the publishers of clandestine erotica that you're interested in you will find extensive, annotated checklists and information in general on publishers such as Charles Carrington (Paul Ferdinando), William Dugdale and Jean Fort (Collection des Orties Blanches).