Apparently some councils hire or loan them out, or the RSPCA, or your local animal catcher. Or:

http://www.hotfrog.com.au/Companies/CAT-TRAPS-WA

http://www.traps.com.au/cat_traps.htm (QLD company, don't know how useful it would be)

http://www.instructables.com/id/Cat-Trap/

http://www.trapping.com.au/ - These guys look like they're more in the lethal trap business, but they might have something, or know who you could contact. Again though, QLD