This achievement is obtainable after sealing the keyhole in Agrabah, which unlocks the Green Trinity ability. Once you have obtained that, go to the accessory shop in 1st district of Traverse Town and perform the green trinity inside. Climb up the ladder that is pulled down to enter the synthesis shop. By now, you should have obtained enough synthesis materials from enemy drops to make at least 1 of the available options.
Side note: you must make each item 1x to unlock the ability to make the ultimate keyblade for Sora, so I would not recommend making more than 1 of each item to help save supplies and reduce the grind for materials at the end of the game.