I would definitely recommend having someone custom make one for you. Obviously there are loads out there you can buy but with the number of craftsmen about, I don't see why you would choose to buy a generic sheath! I'm sure you'll find many offers if you look locally in your yellow pages or something. There might even be a few in this forum. This place that does Bushcraft Knives recommended me a few when I sent them an email, really helpful guys.

Hope that helps!