You can steal a Ragnarok and an Ultima Weapon from the third tier in the final battle. In the original game, this was kind of worthless, but since you can create a clear game save after you finish the game in the Advance version, you get to keep the Ragnarok and Ultima Weapon you steal. So yes, you can have unlimited Lightbringers and Ultima Weapons (and Souls of Thamasa and Master's Scrolls, but that's a different matter).