Ok so I know alot of people know this, and might make the prices change, but heres how to get alot of Olpad/Copernia/Goldania Fast

Requirements
-Weapons (Of course)
-Able to play through part of Innocent girl C/B/A
-Time

First head to the GRM shop located on Parum
Start the mission Innocent Girl
Play through the mission a few times, this will get you some good EXP and Money, but the most important part of playing it through a few times is it unlocks the doors, behind the doors is : Silver Badges, Bronze Badges, Olpad/Copernia/Armania. These are the items you are looking for. If you are playing on Innocent Girl B then you have a change one of the monsters will drop a Goldania. Which are an expensive item.
Olpads and copernias are going for around 20k-30k Meseta a piece, which will stack up if you sell enough. Be Prepared for price wars, This is a popular item!

Have fun!