I just passed last week. In prep, I used some primary care PNP cert exam prep books. Honestly, I wouldn't spend much time on primary care. As you've learned, there is not much out there to help prepare for the acute care PNP exam. If you have any PNP friends, see if they have any books that they could loan you. A friend loaned me her HLA acute care PNP prep book. It was old but still helpful to study. I would also refer to the Harriet Lane a lot.
I found I became too mired down in the minutiae and really way overstudied some things. Of course then there were other areas where I wished I'd spent more time-renal for starters. It's hard to tell you how to study since the field is so broad. I did find the $75 PNCB practice exam helpful. I didn't really think the NAPNAP primary care PNP prep course was very helpful for the acute exam, which of course is not its purpose.