Like Ancient Heart, Blood of Ch’thon and Tainted Brain Matter.
Cronley drops Tainted Brain Matter pretty often which could be traded for the other ones but are there better methods to obtain these?
Farm dynamite chests. Some good locations are mountain deeps and Gloomwald, where you get one in the overworld and one in a cellar.
Another way is to farm aetherial crystals. Then combine those to make aetherial shards. And from those make lots of dynamite.
Then dynamite blue epic items you have sitting in your stash that you won’t ever use and occasionally you get a heart, brain, or blood.
Once you get a key then the blue items you find (on your challenge dungeon run) that are trash then you replace the epics that you dynamited that you weren’t using anyhow. Still got to farm iron bits and shards and maybe some pieces that I just have built up enough over time.
http://www.grimdawn.com/forums/showthread.php?t=57405
You always get the treasure trove in this run plus you may find one or even 2 nemesis (Kuba and Reaper) which can also drop rare materials and / or other goodies. It’s quite fast, unless you encounter the nemesis, ofc.
As for crystals for dynamite making, i usually opt to go to Warden’s Laboratory rift and go back until the shrine: usually net’s me about 10 - 12 aether crystals per run plus you may find Valdaran’s nemesis on the way: very fast if you don’t meet the nemesis.
There’s a second guaranteed trove in the cellar near the gloomwald entrance. You can also get a Barrowholm bounty for a wraith hero and Avris Marrowill for some more loot.
I just run BoC, I usually get the mats for at least one new key. Today I got enough for three.
For skeleton keys you could also farm Grava, he drops blood, so does everything on the way to him and his MI are great.
I did (okay, still doing) this method. I could craft 100 skeleton keys the next time I sign into the game if I wanted, because the drop rate is really good.