I just passed by the National Library on some other errands and for curiosity sake I had a look at Slipinski and Escalona's 'Australian Longhorn Beetles (Coleoptera: Cerambycidae) Volume 2'.
On page 455 it has another Tropis beetle that could be a closer match, called 'Tropis exilis', but I'm not entirely sure.
Either way this individual certainly appears to be a significant sighting....
I don't know Tropis exilis, but I see in the book you mention that its type locality (where the original specimen was found) is cited as 'Moreton Bay', i.e. Brisbane, so I'm reluctant to call it that species. Having said that, I see that the type locality for T. roei, which also occurs locally, is 'Swan River', i.e. Perth! Tropis lepturoides is a third local species in the genus. Regards, Kim.
Roy, I have examined specimens of Tropis exilis in ANIC (CSIRO Canberra). You are right that T. exilis is a closer match, and in fact there is a specimen from Black Mtn. The species ranges from Qld through NSW into Victoria.