@jamesmhoy You could still utilise leftover keys or purchase them between June 28th to July 4th. The keys stopped dropping on the 27th when the event ended, which is why you haven't seen any. We hope that explains it, more details in our article here: http://ubi.li/OcGDZ.
The maintenance has been completed!
20 Standard Cache keys were granted to all The Division 2 players to compensate for the missing Apparel Cache keys.