Since you are in Sydney you might not be too far from Brookvale (Northern Beaches). I use these guys all the time as they have a huge range of screws, etc. If you know the sizes you might just call. I often go in with somethng odd and they just figure it out. I've never failed to get something that works though it might not be an exact replacement.
http://mobile.yellow.com.au/nsw/broo...onlineRedirect
Peter