There isn't much out there as far as exam prep materials for the 2-day specialist classes which includes the CCAS. If you go to pricelist.checkpoint.com you can buy an e-copy of the CCAS courseware for $400 USD. Keep in mind the major focus of the class is the management API, other APIs such as the Threat Prevention API and the Identity Awareness API are only briefly mentioned. Also the class (and therefore the exam) was written circa 2018, and as such covers the early version of the API (v1.2 and earlier if I had to guess).
When teaching the CCAS class here are some free additional resources I pull into the class and present to more fully flesh out the basic concepts presented in the courseware, these should help you prepare for the exam:
Management API Best Practices TechTalk and Q&A
Functionality - API vs. SmartConsole
Working With Postman
How-to use Postman with R8x Security Management API
Automate your R80 Management Server using Ansible
Gateway Performance Optimization R81.20 Course
now available at maxpowerfirewalls.com