The short answer is that you can't get there from here without major modification to the Mosin stock and metal barrel bands assuming it is a Russian. Easiest to do so would be using some sort of the older Mauser barrel bands 93,94,95, 96 with the underlying lug rather than the German 98 and similar variants. If you have a Finnish variant, they did something like the older Mauser mounts for their Mosin variants but they substantially redesigned stocks, barrels, and other hardware to fit their rifles.
I agree that the cheapest is to simply buy a Mosin bayonet.