The simplest solution is to get a longer bayonet, I can't tell you where to get one, but it should be easy and less expensive than a new barrel, since your purchase is an H bar, the barrel is machined flat not tapered, and can take the gas blocks with bayonet lug, not in the original location. The triangular hand guards were not made for the carbine, so round or M4 is the game.
Get an original bayonet, and have a longer blade welded to it in a good profile, and you will have what you want, minus the triangular forend.