Once upon a time there were pearls on the individual prize tiers during the Fort event.
But I haven’t seen that since Spring season last year.
They also have taken most of the turret shards off of the season trees and for the most part replaced them with gold chests (plus the Harbinger stone, which took a spot).
Basically they are going more and more to a “gold chest only” source for everything you need. Since gold chests drop randomly it becomes very hard to plan and control what supplies you will have and when - unless you buy so many gold chests that it becomes a statistical process (which I think is the whole idea).