Inspiration! We need a "Master of the Hand". A twisted Crafter of metal. A forger of Blackened Iron and Blood Soaked Steel. A maker of weapons most foul and armor that makes the very light itself hide in fear of the oncoming darkness.
Yes it would be really nice to begin a line of production of corrupted stuff.
Maybe some items and use and abuse from the merchant contacts and slowly corrupt the abroad to make it easy for the taking.
Maybe the own woods can become so corrupted that we will begin to use it to create:
dark arrows (dark wood plus whatever corrupted meta) siege machines
or, as we are quite subtle. crates, crates that slowly corrupt what it hold, crates darker as the night that is perfect for smuggling.
One thing that i was thinking: The common folk knows where is the fell shore labyrinth? or just the rebels? or only the angel?
If all of the province knows about it we will only have two options.
1. Abandon it.
2. Make it even larger and fearful, hide a bunch of resources there together with acolytes, undead and black imps and let the word spread "There is treasure in this unholy land, someone want's to test who has the purest or the darkest heart, or who is truly worthy"
Make it like a game,(greedy cave, enchanted cave for example) people go there trying to catch treasures and they know that the deeper they go, the harder it will be, and that the maze crush harder large groups
Some will leave and spend their gold showing their nice new helm, some will perish, and be used as fodder of the maze, the ones that keep coming back/ the weak willed or the ones that have already a dark heart will be tempted to join our legion.
One day it will "fail" people will know it is a sort of trap, but a very profitable trap. And when the province becomes so corrupted that it can't hide, or we can spread the hoax that the cave is the source of evil and "someone should find the bottom of this unholy hole and kill the source" or whatever, it will be already a huge underground fortress.