Are there any other mythological beings that got a replacement metal arm, other than Nuada, Lugh Llaw Ereint, and Sigurd?
I found these three from the Mythology section in TV Tropes:
The Battle of Magh Tuireadh relates how Nuada, king of the Tuatha Dé Danann, lost an arm in combat and received a functional replacement crafted of silver.
The same tale is ascribed to Lugh Llaw Ereint in the Welsh mythological cycle Y Mabinogion and may spring from the same Ur-Root.
There is a variation of a Norse myth involving Sigurd and his battle with the dragon Fafnir. During the fight his hand is bitten off, but he afterwards receives a fully articulate metal replacement with intricate wiring in place of tendons.