Hi,
Got married in a registry office myself 6 weeks ago. If you want to get married sooner than 3 months you need to go to the registry office itself. We went down to Births Deaths and Marriages 3 times before we got in to make a booking. All these places have quotas.
We finally got our appointment, though it a was really frustrating and annoying experience, to give notice we arrived at the Queensway offices at 3am only to find, yet again, mainlanders sleeping there and taking all the quota spaces. They are an organised group. Depending on the quota, they arrange for that amount of people to go and sleep there. If you want one of their spaces you have to pay them. After being there 3 nights we finally caved and paid a guy $200 for his spot. We met a guy who had been down there every morning from 4am for 7 nights and still couldn't get a spot.
It is really frustrating, the police came but didn't do anything to move these people on so there really was no other way for us to get a spot other than to pay them!!!!!
Anyway, hope this helps and good luck.