In the 90's many isolated communities removed ULP from the bowsers and only sold Avgas and Diesel. I assume that it was 100LL but I don't know that for sure. Petrol sniffing stopped almost overnight as the Avgas available didn't cause intoxication.
Around 2000, all leaded fuel was phased out from sale in Australia. If the main problem identified with the current round of sniffing is lead then this must not have applied to Avgas but either way, the Avgas supplied now must be different to that supplied 20 years ago. Go back to the old fuel and the problem is solved. GA in Australia is in such decline that the small amount of Avgas used is unlikely to impact the environment anyway, whatever it is.