You could also go to knifeforums.com, bladeforums.com, bushcraftuk.com, and britishblades.com, they all have a section in their forum dedicated specifically to sheaths, maybe you could get someone there to make one for you. Or get enough hints and help to make your own. There is also kydex, which I think is a really neat material for a "working" sheath. They also discuss that material on that forum.

Blademechanic.com is a custom kydex builder, from his website, and my e-mailing to him, it appears that his prices are very reasonable, and he will build anything you want, as long as it is mechanically possible.

Be prepared, 'specially with leather, to pay A LOT more for the sheath than you paid for the knife...