well, ive been out of the loop for the better part of a decade, so my memory is a bit foggy...
anyways, i thought i rememberd a whiles back that there was a custom blade maker, specialized in machetes, hawaii-based i think....
anyways, these were closer to the thin-bladded typical machetes, not the various thick-bladed versions that we see quite a bit of nowadays.
I think some of those came with a saw back, that supposedly worked fairly well, but then again, its using the full lenght of a machete, and due to the thin steel used in the blade, made it much closer to an actual saw...
perhaps the name was something like aki? i think i read an article in one of the magazines, but, well, this was at least 5-7 years ago, maybe longer...
but, yeah, i think thats a special case, i cant see them being too generally useful on most fixed blades.