I usually just ask in the local hardware stores near where I live in Happy Valley. There seems to be a lot of those little hardware stores in Wan Chai too so maybe just go in and ask. They probably know someone if they don't do it themselves.
The other day I had a security gate that needed repairing so I just asked the locksmith downstairs and they came and fixed it for a small fee.
Otherwise I have a really helpful agent who usually helps me organise things like that - can you call yours maybe?
You can try a shop near Starbucks at Leighton Road, they sell locks and stuff and you never know if they do stuff like that too. There's also some small "shops" on the street next to Percival Street, good luck!
