My close friend just recommend me this tuition agency called Schtutors.com. They looked like they just launched the group tuition - SchTutors Tuition Agency | Group Tuition Classes
I have not't tried it myself though. Price is a bit expensive, but the tutors are all teachers. Apparently, they only recommend MOE teachers!
Let me know if you have engaged their services. I am interested in one of the group tuitions for my boy.