Keep in mind that obtaining a Prism Scale is a difficult task in Brick Bronze, as it's a rare item obtained through various means like:
* Rare chance of finding it in the wild: You can find it in some areas like the lake at the top of the waterfall route.
* Trading with other players: Some players may be willing to trade one for other valuable items.
* Winning certain events or contests: Events in Brick Bronze sometimes offer Prism Scales as rewards.
Good luck on your journey to evolve Feebas into the beautiful Milotic!