I don't think there was an ISA-provided BCMA study guide when I took the test. I do remember a long lost of "read all of these books". Some I had read, some I hadn't. I reached a point where I realized this is more of a "life learning" kinda thing and I was either gonna pass or not, so I just took it.
Having said that, I recognize that some people, smarter than me, struggle with taking tests more than I do. I don't think the BCMA was an extremely well written test. Lots of "gotcha" type of questions. I don't remember any exact examples (and wouldn't be allowed to share if I did)...but just pay attention to wording. There were several questions that I thought could go either way if I could argue my point...but I couldn't, so I had to tell myself just KISS ... use the language to figure out what the test writer had in mind.
Honestly, I think you are either ready or not. I'm not sure how I would tell someone to "get ready" for the BCMA test in, say, 3 months. I guess read as many books on the list as you possibly can!