Use local agents. Internet listings are not reliable, many of them are fake and old.
Within a 5 minute walk from a building you like, you will find an agent. Sometimes they are even in the ground floor of the building or across the street. They will not only know what's currently available but often what is coming on the market in the next few weeks.
We did that for a few places and then went back to the corporate agent and asked why we were able to find more apartments in our budget and neighborhood in 1 afternoon than they had in two weeks. This should motivate them. They would rather split commission than lose it entirely.
I'd also agree Belcher's is a good place to start. There are a few agents just across the street from the main entrance (right outside of the MTR exit).