If you have access to a milling machine you could MAKE a bolt with relative ease. Look closely at the Bizon bolt pics - you'll see that the tube on top is actually press-fit into the bolt body! The obviously took the easy route and machined the bolt out of a solid block then installed the tube after the mill work was done. Pretty simple when you think about it! Looks like the charging handle was installed afterwards as well, hard to tell.
Hardening would be the only concern, you'd need to harden the area around the bolt face.