Gonna try my best and answer both at the same time.
But CPA Australia mostly done on self study, does anyone actually goes for revision class?
Self study would suffice in my opinion. I did try attending the revision class for the GSL as per some of my ex-colleagues recommendation. After going through the 6 lessons, I realized i'm better off on my own.
What they did, at least for the GSL segment was summarized and run through the study notes and try to spot the questions based on the case study released prior the exams. I did not follow through the facilitator's notes cause I did not agree with her views. Thankfully I passed whereas I had 2 other friends who took the class with me, followed her and flunk. Food for thought.
Anyone knows of mentors who are able to sign off for CPA Aust or Singapore CA (SQP) if I work for them on a part-time basis?
Check the respective association websites for their list of recognized partners, mostly would be accounting firms. Go join them on a full-time basis for the experience. Plenty of managers or partners to sign for you.
Alternatively, you can try attending those networking sessions to seek a mentor.