I don't where u get a moonstone, but to get a sunstone or firestone, sunstone is attached to Solrock if your lucky which is found in the cave with stairs in it, and firestone is in the cave were u have to move the boulders, srry those are my best descriptions of the caves.
I can only help you but NOT Pokemon ruby...
clafairy
use a moonstone
Meteor Falls on the left
whatever level you want because you use a moonstone
There are some in the game alternately if you catch many lunatone you can get more.
i think you get it in meteor falls up some steps
The moonstone is on METEOR FALLS.if you have used a moon stone on you skitty/jigglypuff and want to again use on jigglypuff/skitty then sorry you will not be able to get another one
Nidorina to Nidoqueen Nidorino to Nidoking Clafairy to Clefable Jigglypuff to Wigglytuff Skitty to Delcatty
The zodiac sign of Cancer includes four stones, emerald, ruby, moonstone (the Planetary stone) and pearl. Sapphire is the talismanic stone
moonstone moonstone and moonstone
I have found some moonstone.This moonstone is very pretty.I have a moonstone ring at home.