There are several useful online tuition portals available, such as
www.a-startutor.com. But I recommend seeking out recommendations from friends or relatives, as tutors vary even within the same agency. Some agencies are notorious or even on the 'dodgy' side. Agencies to avoid include Trustlight Tuition Agency (more like Distrust Light in my opinion). Hired tutors for my son from that agency once, and the agent (his name's Jason Tan I recall) kept switching tutors month to month to earn commission from the 5 or 6 tutors we had. I found it to be very disruptive for my son's progress. The agent resorted to coercive methods and went on to blackmail me when I told him I wasn't keen on continuing the assignment. Almost had to file a police report on that. That was a nasty experience.
So be careful when you contact these agencies! (It's better to contact tutors personally if you know them. As the agents tend to 'jack up' the rates to earn commission)
All the best!