I would just goto a few of the knife websites out there and search for something that looks like it would work.

http://www.knife-depot.com/knife-sheathes/
http://www.ebay.com/itm/Busse-Combat-Kni...=item35bfad1717

there are a lot of good options out there, not GREAT ones like the custom leather you can get, but lots of good ones.