Bonemold is a weaponsgrade material in the metalsmith's forge. It cannot be used to make furniture or "Other Items", so if you were looking there you won't find it. It should appear immediately above Bloodsteel on the weapon material list.
Bonemeal can also be made at the kiln, it seems, at least for orcs. Unless these files are a little broken, which is possible.
Notably the Tribal Warcrafter does not actually use bonemeal. He crafts items directly out of bones, skipping that process entirely, but produces bonemold weaponry, with all the quality and strength of that material (being roughly iron-grade), as opposed to that of mere bones. Bonemold bar production is intended to be a little bit more advanced and involved than the warcrafter, and is of primary importance when utilizing the orcish factory to make weapon moulds, but can also be used at the forge directly.
Once you have an amputation theatre up, honestly you're going to find yourself drowning in bonemeal. Which is good because bonemeal is a flux, ingredient for bonemold, and a fertilizer.
