RTF is a global modification that replaces all towns in the game.

Also, perhaps these dwarves mine nitro-containing minerals in the mines, which are found nowhere else?

No, orcs also live in the mountains, but they might consider these minerals to be trash... it's still better to make a magical herb/mushroom, because the dwarves will live on the herb.

In any case, in fantasy, there are usually many kinds of cool magical herbs (unless someone is lazy and attributes magical healing properties to buttercups and wheat! Yes, yes, Todd Howard, I'm talking about you)

Added 6 minutes later
The mushroom could also be very common among dwarves, some kind of "dragon mushroom" that glows orange in the dark, dwarves grow it on windowsills instead of geraniums, make dye from it, brew beer, and on the surface it withers and doesn't take root.