Sorry to spam, but I just found out exactly how they caught the cuttle - it was picked up when they were trawling with a net through seagrass and other shallow areas around Straddie Island.
Since you mentioned you don't have a boat, it might be a bit hard. Hmmm. Have you tried asking at Pet City at Stafford? We go to them for all our aquarium inquiries, the staff know what they're doing and are more than happy to help, and we've never had a fish supplied by them die of disease or stress. They do stock cephalopods but you'll have to ask as they don't come along all the time. They could probably put you in touch with someone who could help you out with a cuttle.
Let me know what happens, though. I haven't got a proper ceph tank set up yet but I'm aiming to have one by the end of this year. It'd be good to know how another Brisbanite goes with setting up a tank!