According to a sidebar on p. 219 of this work, Green Ronin was going to provide a web extra detailing the cults of the other eight lords of hell. Did this ever get released, and if so, where can I find it?
IIRC we did release two of those as web extras. When we rebuilt our website a few years ago though, a bunch of the old support files went missing. Many of those files are here (http://grfiles.game-host.org/), but I don't see anything for Book of the Righteous except previews.
I'm not sure if this has what you're looking for, but I've just cleaned up Aaron's Tree of Life pages, which include quite a bit of Book of the Righteous goodness, including links to two BotR preview PDFs: