They wouldn't get crushed in a standard hard-shell suitcase. You ought to be able to get a couple of used ones fairly cheap at a second-hand store. They might get bounced around a bit, so use bubble wrap or something similar (crushed newspapers might do the job) to cushion them. I think they'd arrive in salable condition.

That said, I seem to remember some good donuts last winter (June, to avoid confusion) in one of the food areas below street level off the Queen Street Mall. I'm surprised there's a market for KK in Brisbane, but if you say so...