The Final Fantasy Wikia had a list of all DLC, including in-game retailer bonuses, but it turns out most of the retailer bonuses were timed exclusives and are available for purchase, at least in North America:
Weapons
- Seraphic WingNA, JP: PSN/Xbox Live purchaseNA, preorder from Lawsons or HMV
- Genji BowNA: PSN/Xbox Live purchase, preorder from Gamestop (if a Power-up Rewards member)
- Calamity/Catastrophe BladeALL: PSN/Xbox Live purchaseNA, preorder from Square-Enix onlineALL
- MuramasaNA, EU: PSN/Xbox Live purchaseNA, preorder from Amazon.co.ukEU, bundled with Nordic editionEU
Costumes
- Summoner's GarbALL: PSN/XBox live purchaseNA, JP, Preorder from Gamestop (if a Power-up Rewards member) or EBgamesNA, Preorder from GAME.co.uk or bundled with Nordic editionEU
- Battle AttireALL: PSN/XBox live purchaseNA, JP, Preorder from GAME.co.uk or bundled with Nordic editionEU
Accessories
- Diva Mic and Diva HeadphoneJP: Included with "Yakusoku no basho" single
- Goddess' Bangle and Goddess' EarringsJP: Included with mini-soundtrack
- Stiltzkin's Journal and Durable Stiltzkin's JournalJP: Included with Famitsu Weekly Issue #1203
Monsters
- OmegaALL: PSN/XBox live purchaseNA, JP, Preorder from Amazon.comNA, Preorder from GAME.co.uk or bundled with Nordic editionEU
Notes
ALL: Available in all regions
EU: Available for the European/PAL region
JP: Available for the Japanese/Asian region
NA: Available for the North American region