Best chance to get Leather Armor is If you pull and kill the lvl 66 Guardians of Zek. They are really hard with a very good Lvl 60 Group. If Vindicator is up, you cant pull them.
2 Pop near Vindicator, 2 Pop in the Statue of Rallos Zek Room and 6+ pop in the secret Tunnel from Statue Room to Arena. 2 Temple Guardians are between the Vindi spawn and Statue Room. 2 Armor of Zek are inside Statue Room. (if Statue is up dont pull Statue Room
)
With a Lvl 60 Tank (using Defensive) you need at least a Cleric and a Druid with the Druid CH till they are slowed. They can drop 0 - 3 Pieces. (Drop Ratio till now for me was: 5 Plate, 4 Silk, 1 leather)
Verant really should Raise Leather drop Rate, I want to twink my Druid and my Bst.