Board Thread:Questions and Answers/@comment-29958019-20160913043758/@comment-26113680-20160913061622

You can check the Norn database for the collectible Field Materials, each mission is listed there according to scaling difficulties.

I believe that you can get the Duralumin Steel on Rank 4-6, alternatively you could search for a mission that has Duralumin Steel as its rewards and try to repeat it until you get one.

As for Yaksha fangs, I don't know for sure but I think you need to break the head to get it. Plus, just like in case of the Duralumin Steel, you could look for a mission that has such a reward.

Also a general tip when looking for materials. Check the Rank of the item you want to craft, you have to search for materials on the Same ranking missions to be effective at least.