If you can't buy it, steal it from the boss. Weapons throughout Final Fantasy VII Remake offer something special for each character.
While one weapon can act as a good all-rounder, such as Buster Cloud's sword, others allow you to prioritize certain aspects of character play, such as metal knuckles, which play on Tifa's high offensive power, or the mithril staff, which further enhances the magical power of Aerith.
However, one weapon that is easy to miss while playing through the game is the bladed staff. This is one of the most unique weapons in the Final Fantasy VII Remake because it is the only weapon that is not obtained by collecting it in a chest or through one of the shop vendors. In fact, if you haven't been paying attention during all the boss fights, it's very easy to miss it completely.
Weapons can only be obtained in one way - by stealing them from the boss.
In order to get the bladed staff for Aerith, you must go to Chapter 11, which runs all the way through In the railway graveyard. First, you have to fight your way through the level until you start approaching the Sector 7 pillar. At the very end of the chapter, a cutscene causes Aerith to temporarily separate from the group before coming back together to fight the boss Eligor, a ghost who rides a skeletal horse and carriage and owns the staff you want to steal.
Before the fight, make sure you have the equipment to steal materia. If you don't have this equipment when a fight starts, you can restart it from the last fight in the menu and it should take you right before the fight.
Stealing materia isn't a definite hit, so it's like you'll have a few failed attempts to steal it. As she is the most agile, but probably the least useful in a fight due to the resistance of the boss, tifa is the best of the thieves. Eligor doesn't need to be dazed to steal it, but with enough tries you should be able to take it out of his hands and you should now have a bladed staff for Aerith at the end of the fight.
His ability, Shiny Shield, can be very useful later in the game against projectile heavy enemies and bosses, so it's worth grabbing onto this even if the base weapon's stats are less than impressive.
