Here's a little something from a reviewer on Amazon:
"AD4 v. TD4 First off, this is the AD4 pedal (A = accelerator), which is different from the TD4 (T = turbo). The difference is that the AD4 is shaped so that the chain is hooked around bearing with a half circular shape that gets straighter towards when the beater gets close to impact which makes it easier to play faster and get that extra speed at the end of a hit so your foot has to do less work. The TD4 is a half circle shape so that your hits are more consistent, but takes more effort from your feet to go at faster speeds. A large majority of drummers use the AD4, which is the general standard most pedals are built. Some drummers, like Travis Barker for example, use the TD4 (single pedal though)."
http://www.amazon.com/DW-DWCP5002AD4-5000-Series-Pedal/dp/B0075J8AGK
There's a DW 9000 double on aus ebay right now: https://www.ebay.com.au/itm/DW-9000-Series-Double-Bass-Drum-Pedal-w-Hard-Case-DW9000-9002-DW9002/122864833010?hash=item1c9b5091f2:g:aIMAAOSwDkVaNRfG
You may get lucky and get it for a good deal. Will hold it's value better than any new pedal.
If you don't want used gear, you can buy a new DW 5000 from amazon us for around AU$570: https://www.amazon.com/5002-Accelerator-Double-Bass-Pedal/dp/B0075J8AGK/ref=sr_1_1?ie=UTF8&qid=1513492433&sr=8-1&keywords=dw+5002
If you don't wanna buy overseas, a Mapex Falcon or Pearl Eliminator double is around AU$570 new. Great pedals.