Most reliable tutoring centres require tutors to be qualified teachers, so they don't hire undergraduates. I've heard of people working for Northshore before, but I called the one at Chatswood and either only some branches hire undegrads or they've updated their selection criteria, because the woman told me I need to have a teaching degree.
You can apply for a small tutoring business which matches you with students, but there's really no difference between that and doing your own private tutoring. If they pay you more than $30 per hour, or provide useful teaching resources, then you can consider it, but don't fall for one of those scammers who just finds you a student and takes half of the money. Also, there was that story on Tutormaster, a company that disappeared after owing money to many tutors.
The third option is private tutoring. Post ads in newspapers, online, etc. The advantage of private tutoring is that you can be flexible. You can arrange students to come to your home, or you can go to theirs. You can teach however you like, and get paid in cash at the end of every lesson. The only problem with private tutoring as far as I'm concerned is that nobody's going to advertise for you. You need to convince your students that you're capable of tutoring them. But that's not hard if you've got the grades.