While some of these, Crimson Armor, may appear to be items or things you can equip early on, they are not. With the exception of the Sephiroth Summon, which is actually a summon, the rest of the items are all exclusive to the World of Final Fantasy Coliseum. You unlock this after a couple of hours of game time, you can’t miss it. A Tonberry will appear and introduce you to the Coliseum. Likewise with the Sephiroth summon, it is not available until you’re introduced to the Girl Who Forgot Her Name. Both of these are integral parts of the main story so you cannot miss them. If you’re still looking to find your DLC items just push through a couple of dungeons and you’ll get there