The headgear certificate/coupon is a random drop from the cache box. A key must be used to open the box and that can be obtained from any of the following: Kafra Mall, MVP, Job change quests and some other few sources. More info on the cache system can be found here.
I hope this answers your concern.
Why is this buried in a 3 month old thread? How many different headgear certificates are currently available in the Treasure Caches? Could you define "Rare" as a drop rate? How many people are willing to hunt Treasure Caches then buy bronze keys in the hopes of getting the specific certificate for the hat they want to make? Which MVPs drop Certificates? Are they also randomized?
Classic is a patchwork of customizations and modifications and even the veterans are having a hard time finding the necessary information. New players are at a complete loss. Nobody should have to wade through months of patch notes in order to play. You make it very difficult for people to give you money!
