There are a few problems to consider:
1. The Patt 18 scopes are hard to find now in good condition and fitted with the correct rings.
2. If you find one without Aust. pattern rings, the scope has to be dismantled to fit the rings, if you can find them.
3. The process of fitting the scope involved a collimation process in which the bases were aligned in a special jig and the scope is aligned to a Mean Point of Impact on a target using the settings on the iron sights. You cannot just whack a set of bases on the rifle and go for it, if you intend to shoot the rifle seriously.
4. If you could get the bases, you MIGHT be able to use a modern optical collimator to help adjust them on to the rifle to suit your scope.
5. Bedding in an Aust sniper is a bit different because of the heavy barrel.
I suspect one of the reasons for the tiny production of the originals was the arcane set-up procedures necessitated by the Patt 18 scope and the engineering decision to copy pre-WW1
German
sporting scope mounts.