If you are struggling to find Fae Iron, here are some steps I used to get mine. Increasing your luck is extremely important during your hunt.
First you want to make sure you have the Mining Luck perk attached to your Pickaxe. This can happen from crafting your own items with perks chance attached or purchasing them in the trading house.
To further increase your odds, you can craft the Herb Roasted Potatoes to give you an additional buff, the locations for all the ingredients are seen above.
For the full process, of how to find Fae Iron, and be more lucky while doing so, check out the full video in the link below.