Astria Ascending (JP)

There are a total of 88 total items in the game to collect for this achievement, though it may only be 87 - I'll get to that in a second. All of the items will generally be available as drops from enemies or purchased in the town shops. There is one somewhat secret item shop in the Archipelago (the area where you fly around on your griffon). Head all the way to the very SE corner to find a glowing Mig character to purchase some ores that you can't find anywhere else.
 

Back to what I mentioned above about possibly getting the achievement at 87/88 items. It appears the Bronze Stone item (#86) does not always drop from enemies when the Tower is under attack as it should, but one of the game's patches appears to have removed its requirement. If you don't have it, once you get to 87 items, save your game and reload it - the achievement should unlock.

Note: This save/reload trick may be required for some of the other collection achievements once you find the final items you need. Keep it in mind.