How about dropping Trace of Madness crafting materials in quests. These include Watcher's Eyes, Polished Stones, Adhesive Slimes and Brain Samples.

I know you can get them in Reign of Madness adventure pack but what about Harbinger of Madness and Disciples of Rage adventure packs.

Could drop them in the chests, end rewards or similar to Reign of Madness.

Personally id prefer if they where dropped in chests.