the only way I can think of is to build the box yourself.
find a box big enough to fit the 1.5 or 2 cases inside.
find 3 plastic bags that fit over your case. make it slightly bigger than that.
get a couple of cans of expanding foam.
build a wooden box the size of the case + 2 inches on all sides.
place 2 1.5 inches wide by 1 inch think planks across the case that is not length wise but width wize to support the case
now.
put one plastic bag on the case and tape it good .
place one empty bag in the wooden box and empty one or two cans of expanding foam inside. tape the bag shut and spread the foam inside evenly to cover all the box
put the case inside before foam expands and harden, so it rests on the support planks and let the foam expand and harden.
once done repeat with second bag and turn the case upside down.
once done and dry you should have a 2 perfectly matched shapes that would fit in the carton box.
use knife to trim the excess foam where needed.
pack up the case and ship it
the difficult part would be to sell it for the price that covers all the work you need to do.