In
Middle-earth,
mithril was found only in
Moria, according to
Gandalf. (
Tolkien discarded an idea that it once might have been found in the
Ered Luin.) It seems to me that it was more common and readily accessible in
Númenor, though I can find no reference for this: it could be a misapprehension on my part. Tar-Telemmaitë, the fifteenth
king of Númenor, “was so called because of his love of silver, and he bade his servants to seek ever for mithril,” but that neither specifies that it was also found in Númenor, nor that he obtained only from Middle-earth, so it cannot be regarded as a dispositive statement. During the
War of the Ring, some of the Dúnedain wore mithril
armor (e.g., the helmets of the Guards of the Citadel), so some might reasonably have been expected to carry mithril
weapons either then or earlier in the Third or
Second Age. In
Bilbo’s “Song of
Eärendil” that he chanted following
Elrond’s feast after
Frodo awakened, Bilbo says that
Vingilot, Eärendil’s ship, was refashioned in part from mithril, which if true would indicate that mithril was also found in
Aman: the
Elves of Eldamar could hardly be expected to import it from Middle-earth; but Bilbo’s claim may be nothing more than poetic license. I suppose if it was also found in Aman, then before their rebellion, the
Númenóreans might also have obtained some from their friends the Eldar of Eressëa.
Well...the concept of market demand and supplies still work in JRRT's world.
Tolkien was not unaware of supply and demand: certainly mithril was “beyond price” by the end of
the Third Age because of supply and demand, though in the early
Fourth Age,
Aragorn was able to afford mithril in the new gates for
Minas Tirith that
Gimli and the
Dwarves rebuilt for him. Perhaps this was a gift from the Dwarves in honor of his exalted office or assistance from
Gondor in regaining possession of Moria, rather than a “purchased” good: after all, where could the Dwarves find it in any substantial quantity except by recovering it from Moria? (Perhaps they could scour the
ruins of
Barad-dûr for
Sauron’s hoard.)
@Radaghast just hits the point that Mithril wasn't that OP at all.
Yes. As with any other armor, ancient or modern, you can still be bashed to death inside it even if the armor remains unscathed.
Afterthought: Anárion was killed by a stone cast form Barad-dûr. If his helmet was made of mithril, then I think we can safely say it offers no proof against crushing blows.