Only the dwarves are capable enough to repair the gun. Given that they are categorized as monsters, they do not have the ability to tame other beasts or monsters. If they do, then they would have long since wiped out the demons underground and mined all the resources available.
Since they are telling me to fetch the metal to be used for the repair myself, it's the same as saying that the dwarves, whose bodies could withstand the impact of the gun's recoil, couldn't ensure their personal safety in the said underground area.
"So this is the place?"
We descended a shaft through a more primitive version of an elevator, with fences covering the lift all over. After reaching the bottom, only a wide and dark cave welcomed us.
"Yes. The ores should look like this. We only need about 20 kilograms of raw ore, so it shouldn't take that long."