Instructions
Travel to the Tchita Uplands. The Tchita Uplands are south of the city of Archades, and northwest of the Baifonheim Port. Travel from the Cerobi Steppe. Head southwest through the first zone in the Tchita Uplands. Keep going west until you enter the second zone. Run west until you reach the third zone, called the Garden of Life's Circle. Run northwest along the edge of the map until you exit.
Record your data in the save crystal. There is a strong chance you will have to reload your data multiple times. Leave the area and go south, back into the Garden of Life's Circle. Head southeast and look for the tree at the bottom of the map by the coastline. Search to the right of the tree to find the treasure.
Reload the game if nothing appears. The treasure container has a very low chance of spawning in any given game. Press "Start" and "Select," and select the option to return to the main menu. Reload your game and repeat step two. If the chest does appear, there is only a 50 percent chance the diamond armlet will be inside. Keep resetting and reloading until the chest is there, and the proper item is inside. This is the best method to get the diamond armlet early in the game.
Buy it later in the game. Purchase it from the Traveling Merchant at Dalmasca Estersand for 20,000 gil. Make sure to get the Treaty Blade from Occuria in Giruvegan first, as the merchant will not have the armlet until the sword is acquired. Dalmasca Estersand is found directly east of the Royal City of Rabanastre.
Fight Mom Bombs. Travel to the Great Crystal inside the ancient city of Giruvegan, located in the far south of Ivalice. Walk inside to get to the Gate of Fire. Activate the waystone to teleport inside the crystal. Find and fight Mom Bombs. They have a small chance of dropping a diamond armlet.