Finding Weapons during quests.

[MelonCarty]

This is a very rare chance, but it will happen. If you mine long enough you can stumble upon a ? mark logo item. Its not garbage, but a piece of rock hiding something.(Rare of 5)

Usually it will be a weapon, it will be random, if you get a rusted sword upgrading it will make it the Ancient Sword, but at times you'll get common weapons like Iron Sword, so you have to get lucky.

Place that I found it is in the Volcano area(once you hit HR 18 you'll be able to explore online there)

[Jackrack]

Ya Kinda like Ruststones and Ancient Ruststones in MHF2 and MHFU. Though I haven't found any in MHTri yet.

[Sihk_Sketch]

I've found a lot of these.
I usually sell them.
The only one I've kept is the Rusted hammer. I have it upgraded to breathcore now and I only need a Rathian Ruby to make the Lava core!