Looking for a German language teacher in Singapore

My son is interested in learning the language but as an person doing his internship in a hotel in Singapore, he cannot be sure about his timings as his shift changes almost every week.

We are looking for a teacher who is prepared to have a flexible teaching schedule - we visualize an arrangement where the tuition is by appointment suitable to both parties. Do you know any teacher in Singapore who would be prepared to take a student on these terms?

The focus has to be on conversational German. Certificates of having learned German are not essential.

I am in contact with the Goethe institute here but doing it with them will cost me a hand and a leg and some more.

Any suggestions?