I have (and will continue over the next couple of weeks) entered a bunch of National Engineering Landmarks / Historic Engineers Marks / etc as virtuals.
I will only enter ones for which I have a confirmed coordinate / marker combination, so it could be that I won't be able to get them all.
My main sources are crowdsources from GA3049 and GA2720, the Internet and the Heritage register at the Engineers Australia.
The Heritage register is in an interesting state of confusion as there has been some confusion in it about which are Engineering Heritage National Landmarks and National Engineering Landmarks (spot the difference?) and which are Engineering Heritage Markers and National Engineering Landmarks. In the beginning everything was nicely sequentially numbered and then they stopped numbering them after a certain date. And then I have a list from July this year which does not have the numbers in them at all nor links to the nominations and reports but seems to be most up-to-date with the recent ones. Oh well, that is life.
Happy hunting and let me know if you find one which is not on the list of GA3049 and GA2720 (with coordinates and pictures please

Edwin