I am not familiar with the PACE certification. I earned my now CAP rating way back when and the exam was very different. I did, however, for a number of years work with CAP candidates and I keep my certification active. If you go to the IAAP website you will find all the information you need about studying and applying for the exam: https://www.iaap-hq.org/page/CAP_Certification
Marie Herman does offer an excellent study program. Her Fall 2022 CAP Exam Study Group has started but new students are welcome any time: http://www.mrhenterprises.com/CAPStudyGroup.shtml
I doubt you will find many free materials. Even in my day, when the current specific study material were not available, we had to beg/borrow/purchase the recommended study materials. Believe me, there were a lot of recommended books at that time. Of course, the exam was very different.
Best wishes on a successful journey.
C. Joyce Hawkins, CAP, OM
Freelance Consultant, Retired
St. Peters MO