You can start with a search on "Singapore" in the
Teach English Worldwide forum. I know there are some jobs there for Singapore. This will also give you an idea on the conditions to expect.
Teaching in Singapore is not yet as developed as other Asian countries, however there are still jobs available if you search hard enough.
Your best bet would be to make a list of private schools and contact them direct. The Singapore Ministry of Education also hires every year to fill positions in the State sector.
The average
teaching salary in Singapore is just shy of S$3,000 / month. Don't forget the cost of living isn't all that cheap.