If you did not loot this when doing the Droga quests (the item is prelootable, and need 1 per character), then you will have to go back to droga and do a lot of killing to get these.
I got drops from other mobs, but the important thing I found was most areas will not give you drops of Dronan Ore.
I had most success in the area where Miner Groundfuse spawns. It only took me about 6-8 kills per ore.
Dubrave