First go to the place in Phon Coast where you see a mess of treasures. Open them all. This will have something to do with the pack of treasures in the Necrohol of Nabudis. Open the tresures at phon coast in a certain way because in nabudis, you will have to open the treasures the same way. I know you might not get the Zodiac Spear because of all this but its worth waaaaaaaaaay better! Then equip Diamond Armlet with one of your characters.
NOTE: Make sure zodiark is dead.
Then go to henne mines and in the middle of the arena where zodiark was, there will be a treasure. After you open it, there WILL be another treasure in its place. Cool huh? Everytime you open this treasure, another will take its place. UNLIMITED TREASURE AND GUESS WHAT? WITH THE DIAMOND ARMLET, THE TREASURE CONTAINS A TOURNESOL, A ZODIAC SPEAR, WYRMHERO, ULTIMA BLADE, MAXIMILLIAN, DARK MATTER, ETC WITH A 100% CHANCE!!!!!!! If you dont equip diamond armlet, then you will only get weak armor, weak weapons, knot of rusts, etc. THIS TREASURE IS SO UNLIMITED YOU CAN GET AT LEAST A BILLION ZODIAC SPEARS!!!! I SWEAR!!!!!!! PLEASE TRUST ME!!!! In truth, I did not get this cheat from other people. I found it out myself. I guess it was a glitch if you ask me but DAAAAAAAAAAAAAAAAAANG!