There is an easy way to get some powerful weapons without actually looking for them. You need one R-Ability, though, which is "Catch," from the Thief class. This allows you to catch any weapons thrown at you by Ninja, which is something you will do when you run into level 90+ ones. One of the best places for this is on the HORROR level in the Deep Dungeon. There is one battle where you run into a bunch of Samurai and Ninja. A good strategy for this battle is to get someone to stand on the lone square that allows access to both sides (Death Sentence trap), which makes it so the Ninja can't come across and have to throw stuff at you. What a Ninja throws depends on his/her level and what abilities they have (sometimes, they don't have access to all the throw abilities).