Complete the game and save after the credits. Then load the cleared saved game file to start a New Game+ playthrough which allows access to the Grade Shop where you can purchase the following items for the indicated amount of Grade. Any leftover Grade will be kept for your next playthrough.
You need to have filled in your collector's book to get access to this shop, which needs at least two playthroughs.
You then need to speak to the purple-clothed man in the library of Daath church to get the Item Collector title. Equip the title and speak to the same man and the shop will then show up near the inn at Grand Chokmah.