You are guaranteed to be able to buy Iru Elixirs that heal a random injury by upgrading a village to a Conclave and researching until you get Alchemist buildings. Building upgrades from Herbalist -> Apocathery -> Alchemist (EDIT - One More Upgrade) -> Alchemy Lab. Also, you can get a Restoration Potion from the quest where the Butcherman butchers the poor old lady, or alternatively you could get lucky and score a Resoration Potion as high-level loot. Restoration Potions remove ALL injuries from one hero, giving them a Medical Makeover. 
