I have found another place that does 3D scans in Perth. Its called... First Photo.
They take people from 7 weeks!!! And you can go in for gender from 14 wks.

I tried calling to make an appointment asap, but they only work 2 days a week (sunday & Monday) and the next available was in June so thats a bummer cause it would be the same week as my 20 week scan..