I've seen the fish shipments in some of the lfs come in, and for the big fish they have them in a Styrofoam box ( lined with fish bag plastic, or a garbage bag) and have that box pack into the cardboard box. One time when i was in they got a shipment of a larger cichlid and there were strips of black plastic in the water to keep the fish calm. I'm sure any fish distributors in your area would be able to give you some better pointers!
Becca
Becca