All these items are exclusive to the post game:
*Some of these items may be found in The Crown Tundra or Isle of Armour
-Every kind of Mint (BP)
-Ability Capsules
-Sivally's Memory Drives
-Battle Tower TMs
-Adrenaline Orb (BP)
-Room Service (BP)
-Weakness Policy (BP)
-Eject Pack (BP)
-Red Card (BP)
-Blunder Policy (BP)
-Sonia's Book
-The Wolf Items *2
-Oval Charm
As you can see a majority of these are located in the Battle Tower and require BP so that's a struggle. You may also be wondering about the Shiny and Catching Charms. Well, actually, they can be obtained during the story if you meet the required goal. One more thing to mention is that a Charmander can be obtained as a Gift-Mon from Leon, not an item but I think I should bring it up. You can also get a Type: Null from a lady in the Battle Tower, this is also where you get the Memories. As for usual if I made any mistakes you can either downvote or post in the comments, but I've made sure to check the information I have multiple times.
Hope this helps :)
*2 The Rusted Sword and Rusted Shield are picked up during the story but don't appear in bag and are only usable after the main story has been completed.
All information has been sourced from https://bulbapedia.bulbagarden.net/wiki/ which is an open source encyclopedia and may contain incorrect information.
