Hi Jeffrey,
The guide Chassain does not exist anymore, it's a pity because it was the best pilgrimage guide ever.
The information it was containing is now divided in a lot of different places.
The start point is, as mentionned by Falcon269, the web of the Voie de Vézelay.
Vézelay to Eguzon:
http://www.vezelay-compostelle.eu/
Eguzon to La Coquille: missing...
La Coquille to Port-Sainte-Foy:
http://www.compostelle-limousin-perigord.fr/
Port-Sainte-Foy to Captieux:
http://www.saint-jacques-aquitaine.com/voie_vezelay.php
Captieux to Hagetmau:
http://www.compostelle-landes.org/index.php?p=vezelay&lng=en
Hagetmau to St-Jean-Pied-de-Port:
http://www.aucoeurduchemin.org/spip/spip.php?rubrique382
I have walk this way in 2007 and have kept the GPS tracks and can provide them.
I was using the guide Chassain. Since them, I have follow the situation on the Voie and very few have changed.
If you need more info, ask....
Buen Camino, Jacques-D.