Hi Jase,
This beer is found almost everwhere, i can't help with exactly where in sydney but it will be somewhere. As far as the beer its not only very good but one of the best beers of the style i have tried.
In adelaide it can be found in even some of the not so good bottle shops, i recomend only buying from a shop dedicated to suppling good imported beer with a good turn around, You pay $9 for a 500ml bottle and the only way i think to insure your getting close to what your paying for is to find a shop that sells a lot of these beers and looks after them.
They have dates on the bottle so check that to start with.
In Adelaide we have one shop that really does deliever good english beer fresh as could possibly be expected and i pressume sydney would be no different if not better.
Jayse