Instructions
Talk to the King of Pandora after completing the ruins and saving the villagers in the first quarter of the game. A guard will move and allow you to access the treasury, where you'll find the level 3 sword and spear orbs. The chests will stay in Pandora in case you miss them and need to pick them up later.
Visit Santa's house to pick up the level 4 spear orb during your first trip to the ice continent. If you miss this orb, it will stay in Santa's home and you can get it when you return.
Make a new save file before you enter the Imperial Castle. This area will close permanently after you complete it, and there are important axe and whip orbs in two chests inside.
Save your game in a new slot before you enter The Temple of Darkness. In this area, there is a sword orb chest that occasionally will have two sword weapon upgrades. If you get a sword and an axe or whip orb, then it means you missed one of the orbs in the Imperial Castle. Restart from your earlier save file if you want to max out all weapons.
Get the boomerang weapon orb from the Underground City before raising the Mana Fortress or it will disappear. The orb is in a chest in the first part of the city where you have to turn off the water slides.
Fight enemies in the flying Mana Fortress to get the hidden orbs that upgrade your weapons to the max level 9. The following enemies randomly drop chests that have weapon orbs: Whimper, Master Ninja, Metal Crab, Terminator, Tsunami, Fiend Head and Wolf Lord. If you are unsure of an enemy's name, then target it with a magic spell to find out. It can take minutes, hours or days to get the random weapon orbs from these enemies.