The Xenomorph from the Alien’s franchise extracts iron from blood of its host. That is where it gets the metal for its teeth. Not explicitly stated in the films but something mentioned in one of the books.
My extremely rough math suggests 282-470 people go into the making of those teeth, assuming xenomorph teeth are roughly 10x the volume of a human tooth (5-6 mL) and that they have thirty of them, no losses, and we're talking pure elemental iron and not a protein/metal matrix or otherwise. Figure 7.8 g/mL as the density of iron, by 6 mL per tooth is roughly 47g per tooth, so in the ballpark of 10-15 humans worth of iron per tooth. Humans have 32 teeth and 30 seems as good as any other number, so 47g/tooth by 30 teeth is 1410g of iron. That gives us somewhere between 282-470 people per set of xenomorph teeth.
I don't know where exactly I was going with this but it was fun to estimate.