The wiki says you can get elementium from rocks golems and alicium from lanterns but none of these seem to drop this anymore so how do you get these items in order to create armor?
The level 50 rock golems are supposed to drop both ores; for some reason they've been bugged since the Nightmare Night update and don't register a defeat-- thus not dropping loot or giving exp.
Alternatively you could try the dragons, they do drop alicium ore but not elementium.
I finally got elementium by farming the high level golems on evershade (the ones behind the Magical Catalyst lantern) and the alicium by killing the level 50 dragons on the Sister's Castle.