I would suggest a boot camp - the exam changed in July 2017. Anything you find on line now will probably be for the old exam. there is something like 2k ISSAPs in the world, so not that may posts. Although the old material should cover you, it did not work out that way for me. The level of details is far more in depth than the CISSP. Good Luck !
I've thought about CISSP-ISSAP as well, and not to throw a wet blanket on it, how much value does this really have? I've been a security architect for about 8 years and can't remember ever meeting anyone with this. Would potential money and effort be more valuable to focus on something like sabsa training?
This security architect certification is an excellent way to hone your craft. But is it right for you?
You’re a great fit for the CISSP-ISSAP if you:
1. Are a life-long learner who craves a new challenge.
2. Want to go beyond the CISSP. You have a competitive spirit and want to stand out from your peers.
3. Want to be seen as a subject matter expert and prove your knowledge in a more focused area.
4. Are looking ahead in your career. The CISSP-ISSAP will help you achieve an even higher level of success.
5. Need this concentration to move into a specific job.
The CISSP-ISSAP is ideal for those working in roles such as:
1. System architect
2. Chief technology officer
3. System and network designer
4. Business analyst
5. Chief security officer
The official text is the place to start. You'll need to read through the references at the end of each chapter (many of these are in the public domain). If you've read a number of the NIST SP800 series, IETF RFCs you'll be in a reasonable good position.