I understand and appreciate that the RAAF received and operated the Vultee P-66 Vanguard, but this wasn't until 1942, if my memory serves me correctly.
So, how about this as a scenario...not happy with the Brewster Buffalo pathetic performance, the RAAF rejects the British offer of this obvious second-rate fighter and instead opts for the Vultee V-48C Vanguard, which itself was being developed for Sweden. The Australian government concludes an emergency order with Vultee, if and only if they can expedite their delivery to Australia, to which Vultee is more than willing and able to do, with the notion that other air forces would follow Australia's lead.
The RAAF impressed enough with the Vanguard, coordinates with the Australian government to have Australian War Supplies Procurement office in Washington for the Licensed production of an improved Vanguard
Hence Australia negates the need and urgency of the CAC CA-12 Boomerang.....
M.A.D