Not a single Evelin crystal in shop for over a week
A single Eveline crystal shows up in the shop every in-game Monday, as the first crystal in the weekly rotation through all 15 base follower crystals.
Otherwise than that, pray that an offer shows up super rarely in your kingdom’s bazaar, or one drops from that day’s kingdom defense, or go farming the Chapter 15 dungeon and pray even harder for one to appear in a chest.
I’ve had 3 of them drop from my last 2 KDs.