The Gondorian Coin artifact can be found in Fern Outskirts, in the southern part of Sea of Núrnen.
Coin, Gondor, Third Age, circa 2920
Merchants across Middle-earth know if it's Gondorian, it's good. And they freely accept these silver pieces (known as Castar) as currency, trading them across the civilized realms and with almost all the races of Middle-earth. This particular coin likely made its way into Mordor through that realm's primary trade route, the Sea of Núrnen.
"It's good. Coin of the realm.
Sure, but it's the coin of Gondor's realm.
If you don't want it…
I didn't say that, Cap'n. But how about a few less of these and a little more of that Elvish cloth you brought over from Eregion?
I think we can do that."
"Wealth will not save Gondor. Uruks do not care for trinkets.
Sauron will use gold to buy allies among the kingdoms of Men."