I own and recommend the model #PK504 heavy duty yet lightweight high density foam shelled case made by Protec. This case is quite rugged for keyboard gigging transport but if you need to ship your keyboard by air, you may need an airline flight approved ATA hard shell case (though unfortunately an ATA hard shell case is MUCH heavier in weight).
Be sure to specify the "model #PK504 case designed for the Technics KN5000 keyboard" and they will supply you with appropriate foam block inserts which will allow the KN5000 to fit perfectly in the case.
Protec does not sell directly to the consumer but they can direct you to the store closest to you.
3040 South Manhattan Avenue
Fullerton, California, USA 92831
email address: firstname.lastname@example.org
telephone: (800) 325-3455