im from W.A also, and when the US/AU dollar was good i bought some cylinders from the US and got them ported and sent to perth (HJR did the porting and rebuild kit, he is one of the sponsors listed in the link above.
Hamish engineering does some port work (they are in welshpool, briggs st) and there is a place in wannaroo that port, one of the members here had some cylinders ported from there, he would know the name of the place. There would be more places that i dont know of.
all the sponsors listed in that link have had so much banshee experiance, it sold me onto getting one of them to do the porting instead of in perth.
the exchange is shit now, so it could get expensive.