I too have noticed since the patch that Underworld Trading has been nerfed (whether intentionally or not) as I have sent two companions out almost constantly on Underworld Grade 2 Metal Quests only hoping for the purple drop Alusteel. I was doing this for 2 days straight and only once today have found a return of 2 Alusteel after probably 100+ missions. The Alusteel is only available through Underworld Trading as far as I"m aware, so it either needs to have a higher drop rate or the items you find in underworld trading should be available as resource nodes throughout the world.