After completing the card "Trial by Combat", you'll unlock the card " The Elder Lizard".
The Elder Lizard card doesn't offer any token for completition, but it does offer this beautiful achievement!
All you simply must do is have metal ore on you before you land on "The Elder Lizard". Failing to have any more results in no trading with her, and in turn no achievement.
A good card for obtaining ore (and for Unlocking the very lucky/ very unlucky achievements) is the "Sunken Treasure" card. You unlock this card from either defeating the Kraken or talking to the Ghost of the Sea once you've defeated the Kraken. This card gives you a handful of chances to find ore among other things (I mean a handful of chances!)