They make tubes that long for industrial shipping, but I dont know how you would find one local, try a google of shipping tubes.
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We ship aircraft hinges in PVC pipe from the local home improvement store. Glue one end with a cap, then either slip on a cap and seriously tape it or glue on a female adapter then use a threaded plug. If you can't get PVC big enough use ABS (the black type). UPS will only take 6' long but FedX will take up to 10'. This will steer you away from the cardboard tubes which can & will be bent or smashed by the bozos that use them for prying bars or whatever at the shipping facility.
Good luck, John