Yes 98 is extremely hard to come by and there are only 2 servos in Darwin I know of that have 98, both are 30kms from here and the price... try $1.75 a litre
A familiar story!
For the past few weeks, I've only be using Vortex 95.
The loss in power is slightly (very slightly) noticeable - but there seems to be no difference in economy. Considering the difference in price between 95 and 98 at the moment (6cents+ per litre, plus another 4-8cents with a Safeway fuel docket) 95 seems the better economic choice for now.