Hello and welcome to Just Answer.
I take it that you have metric sized tires? If so, there is nobody that manufactures them any more so finding them is extermely difficult.
From the description, It sounds like you need the front tires balanced or possibly the wheels may be bent. Ant professional garage should be able to take care of a tire balance for you.
As for a specific shop in Sydney, I can't help you with that one as I am In the U.S. sorry.
BMW Master technician
BMW S.T.E.P. graduate, 10 years BMW dealership experience