I had a hard time finding one, but I found one at a storage place, they have all different shapes and sizes for people who are moving.... If you have ups box it for u it will cost 100 bucks probably, they charge hella money to make a custom box.
Tom, If you have a U-Haul dealer around they normally have what is called "wardrobe" boxes which are a perfect fit for a wakeboard and works great. Regards, The Wakeboard Geezer