"Stump-Tailed Chameleons - Miniature Dragons of the Rainforest" (2004) Peter Necas. I have it and it's a good book; covers pretty much all species (though was before the split of Rieppelleon and Rhampholeon, so a few things, such as the R. brevicaudatus, are under an older name - but that makes no difference). Zoo Book Sales is one place to get it; there are undoubtedly others, but they're the primary US vendor.
Edit: I see you're in England. I think the book was published in Germany; look around.