I make my sheaths essentially like the one shown by stumpkiller, though I cock mine the other direction for crossdraw.
There are a couple of sheaths on that website that appear to be of european design. From the photos it APPEARS that they are made by forming the leather around the blade and running a stitch up the back side, so that it is not seen from the outside. Can't tell for sure. (it also looks like there is a tooled design along the edge of the sheath). There also is no apparent belt loop. One wonders if perhaps there could be an arrangement similar to that found on the sheath of my Finnish filet knife....the sheath is formed in the same way, and there is attached to the upper end of the sheath at the stitch, a ring and belt loop. The knife sort of dangles from the belt.
The only 18th century knife sheaths that I am familiar with are of the "sword-type", with brass tips, frogs, etc....which are also formed around the blade and stitched up the back.