--- Finding the Foundry.
1. Start on the quest "Machines of War
2. Run/teleport to the entrance of "The Battlefields". Head east a few steps. The Foundry can only spawn in one spot. It'll be directly next to the entrance of The Battlefields, slightly east from where you start. It shares a spawn with "Cryder's Outpost" and "Battlefield Stores". Keep remaking until you get it (Foundry is about 10% chance, from what I've seen).
--- Finding Halmin
1. He can only spawn on Foundry Level 1. Clear the whole 1st floor, then reset if you don't see him.
2. He spawned for me in a very small room with only a few beds and a fireplace against the right wall. He crawled out from under he beds after I killed the demons in the room.
3. Others have said that he crawls out from a fireplace when you kill the demons. However, when he spawned for me, he actually crawled out from under a bed, not from out of the fireplace. Not sure if this is important, but theoretically it may be possible to "glitch" the spawn if you accidentally destroy the beds before killing the demons in the room. Food for thought.