OK, this one is a bit complicated:
It requires you to be caught by the bandit lizards, and then to escape and retrieve your clothes. You'll get some "tatters" that you can take to the blacksmith... and then he'll eventually turn them into a new set of armour for you!
You'd have to go back to an old save in order to unlock this, though... so if you don't wanna go through all the hassle, I can say there'll be an alternative way to acquire this one in the future!