Peter Lobner, in his USN nuclear submarine study recognised the low availability of US SSNs, including Virginias. On page 132 Lobner writes:
"In October 2017, the maintenance backlog was reported to have idled 15 SSNs for a total unplanned delay of 177 months (14.75 submarine years)."
So 15 of the USN's 50 SSNs are inactive, in maintenance, at any one time.
On that ratio, 1 of the 3 RAN Virginias of the 2030s will be inactive, in maintenance, probably in a US shipyard, 1,000s of kms away from Australia, at any one time.
This leaves only 2 Virginias maximum active in the RAN.
However, we can go further using the standard naval/military Rule of Thirds indicating just 1 of the 3 RAN Virginias will be availablefor operations on average, for something like A$120 Billion of Australian tax payers money, spent by 2040.