Last April, I bought the ISSAP self-study course from ISC2. It came bundled with an exam voucher and with CISSP refresh course videos. That was the study material I used. I also had a quick look through the ISC CBK for ISSAP and I don't recommend that book. Too hard to read and the material seems out of date.
Further more it helped A LOT that I have a big knowledge and experience of technology with operating systems, networks, cloud computing and security operations.
My advise to those who have recently passed CISSP and are considering ISSAP:
a) Get plenty of experience and skills working with Cloud computing.
b) Make a plan to take the ISSAP exam in 12-18 months after getting the CISSP.
c) I recommend the ISC self-study course.
Now I guess, the next step would to find an ISSAP certified to endorse me. I don't think ISSAP is self endorsed like CCSP, is it?
No, you don't need to find an ISSAP to endorse you. All the CISSP Concentrations are effectively self-endorsed:
NB - the CCSP isn't self-endorsed at all. If you already hold the CISSP then ISC2 act as your endorser with the CISSP being used to effectively waive all CCSP experience requirements. If you don't hold the CISSP then you need to go through the normal endorsement process.