MCYS priorise Singaporeans over expats in allocating kids, so your chances of getting a child through them are negligible. An agent is realistically the only way.
Have you seen this on Aus High Comm page in Singapore?
http://www.singapore.embassy.gov.au/sing/Adoption_visa.htmlThe requirement to be legal in country of birth and "Embassy letter" is why you are pretty much restricted to Singapore. If you adopt in, say, Indonesia it may not be legal there, plus to bring the child into Singapore the Aus Govt have to guarantee citizenship, and I understand there's been a diplomatic row over the wording. If you adopt a Singapore child you avoid both those problems.
If you keep bumping this thread I'm sure an Australian adopter will be along soon.
Otherwise there's a yahoo group "Singapore Adoption Support" and you could join/ask there.
Good luck. You'll find adoption a very different experience from in Australia, I think!