There is always this one:
http://pioneerarms.com/ticonderoga_knife_and_blades.htmlSupposedly a copy of the Fort Ti knife, which is one of the very, very few non-commercial blades that can actually be demonstrated to have been used in the 18th century. It isn't a very precise copy though, as you might be able to tell from the pic here:
http://www.shrewbows.com/rons_linkpics/Ticonderoga_combo.jpgThe original has a belly to the butting edge, curves up in the middle, and drops just a bit at the point. It is not nicely forged or filed to a good crisp silhouette, but has all kinds of irregularities of line and what Gordon Minnis refers to as "shapelessness" - very typical of original non-commerical blades but virtually never seen today. It also had a bone or antler grip with no bolster or ferrule surviving - probably just jammed on and held in with pine pitch/cutlers epoxy.
FYI, The vast, vast majority of knives used in the 18th century where cheap and readily available butcher and folding knives from Europe. I do think that people occasionally made and used one-off primitive knives prior to 1820 or so, but they are way overrepresented in this hobby. Most of the knives shown in the books are cannot be proven to date from the 18th century, and there is a pretty good chance that they date to the percussion period (after Jim Bowie introduced the Hispano-Mexican taste for big fighting knives to English-speaking America) or even as late as the Great Depression.