A mate of mine cathes a bus from chatty to wynyard then a city circle train to central and a bus to uni. Its a bit quicker than taking the train to central alone and then a bus to uni.
I got no idea about a direct bus service but I live very close to u and what i do is get a bus to the city (QVB) and then a bus from there to uni. Heaps of buses go from the city to UNSW such as the 392, 399, 396, L94, etc. There are also lots of city buses that go along the pacific highway such as the Epping/Lane Cove to city services.