I own 2 Greenspeed trikes, both of which I picked up on Ebay. There is a buy/sell section on Brisbane Cyclist where you could place an ad. Bike Exchange may also be worth a look.
The Greenspeeds are a great ride aren't they! I built a homebuilt SWB recumbent many years ago to try out, it worked, but it felt very twitchy. It was another 15 years after that, that I got my first Greenspeed. Since then I have gone even further in the recumbent world and am the proud owner of a Mango velomobile.
Look out for our Recumbent rides which happen sort of regularly, we are well overdue for one at the moment, would be great to have you along. A normal turnout usually includes at least 1 velomobile (sometimes all 3in Bris), 1 or 2 trikes, 2 or more recumbent bikes and a few DF bike-we are not exclusive!! We normally ride to a place for breakfast and coffee. (often meet at Nundah and ride to Redcliffe/Woody Point area and return)
Welcome to Bris Cyclist, they are really nice people here!!