Level 45/50 set: Buyable from the Calamity Salvager in any of the main cities. Gridania's is near the Mail Moogle.
Level 50 i90 palette swap set: Farm Antique tokens from Sastasha (Hard), Qarn (Hard), and Snowcloak and trade them to a vendor in Mor Dhona.

Level 60 set: Buyable for Centurio Seals from the hunt vendor in Ishgard.