Honestly? You might have trouble finding a book that targets Sags, not because the info isn't out there, but because it's hard to know which book would be the right one (and a lot are out of date). There is a lot of info out here though - have you tried Google? Basically, they are tropical - love lots of humidity, light, heat and well drained soil, but can take temps down to 50 in winter. They don't necessarily have specific unique features that make their care much different from other tropicals such as Fukien tea - in fact the two are pretty similar.

Maybe I didn't word this correctly - what I am looking for is a book with general bonsai information that has a chapter or at least a page with advice on the care and best bonsai styles for this kind of plant.

And I did get it, but knowing which (of thousands out there on bonsai) has such a page means either knowing right off the bat that one of yours from ? year has one, or hoping someone else has that good of a memory. Such books usually address many different trees - often one out of hundreds, and so being able to put a finger on which one is very difficult.

I heartily recommend 'The Complete Book of Bonsai' by Harry Tomlinson, which I found in my local library. There is a page for Sageretia which sums-up all necessary information about caring for this tree; I'm new to indoor bonsai, and have found it very useful for its photographs on every page as well as cultivation guides.
Best of luck with your tree!