All the mains are konoha ninjas, so it doesn't really have anything to do with the "lands". As for their elements, it's due to this
Iron is not really a "thing"
Also, LoI is filled with samurais, come to think of it, Mifune isn't really a ninja...
Should there be an "iron" main, it would probably be a samurai, but I don't think there are samurais in konoha.