Special orange pumice stones from the southern deserts. Rubbing it along your skin lets you treat it as leather. 2 days after you use a stone, your skin peels and burns horribly, giving you -2 to all saves unless you spend a day resting.
Each stone can be bought for 100 coins.
 Sit under a waterfall and let the water flow on you while you meditate for 30 minutes. You can also use a fountain or a helper to pour water over you, but it takes twice as long.
As long as you keep mental focus and don't take damage, you can treat your skin's AC as chain. You can learn this from a wandering ronin.
 Gut and skin a forest boar by yourself. You have to kill it with a spear made of wood, the tip hardened in a fire, and twist the pig's innards around a sacred evergreen tree, then bury the boar's skin in a clearing.
As long as no human sets foot in that clearing, you may treat your skin's AC as chainmail.
 Druids of 4th level and Barbarians of 9th level or higher can anoint a 'champion' with war paint. The champion cannot wear any clothes or fight against the interests of the administer of the paint; else it wears off and the protection is lost.
While painted, the champion counts the AC of their skin as platemail.
 You must be accused of a minor crime that you did not commit. The crime's punishment must be humiliating and painful, but not serious enough for long term imprisonment or death.
After enduring your time in the stockade or getting flogged by children, your skin hardens as chainmail. This lasts until people have either naturally forgiven you or realize you aren't guilty.
 Spend a month in silent service to a blind crone. You must grab objects she reaches for, perform basic tasks, and help her get around without ever saying a word, explaining your purpose, or accepting any payment.
If you do, you receive AC as leather until she naturally passes away.
 Knighting Potion. Grants your skin AC as plate and makes anything you hold in your hands glow. Lasts for 3 exploration turns.
Requires the tears of a knight to create, which is required to get anyone to brew these for you. Also costs 400+ coins.
 Turtle-Kin race. Your 'skin' counts as chainmail until you reach name level, and then becomes as plate. You cannot get any bonuses from your dexterity score.
 Magus Shield. Whenever you are about to be attacked, you can 'burn' a spell to increase your AC by the spell level of the expended spell.
 Black mites can be poured onto your skin to infect you. Once infected, the user feels an incredible urge to drape raw meat on themselves for the mites to slowly eat inside their skin.
In return, the mites grant the subject AC as chainmail. The infected smells odd for as long as they carry the mites in their skin, and has an unreasonable fear of cleaning supplies & soap.