Is this Catalina an ex-RAAF aircraft? If so it shouldn't incur any tax. If not then tax would be payable.
Why should QANTAS pick up any tax bill, that was oversighted by any group, (even well intentioned volunteers who haven't done their homework) at the expense of QF passengers, and staff?
In reality you should be asking the Australian Defence Force or the Government to pick up the bill , not private enterprise.
No sympathy here, I am afraid.