Lack of Iron
The lack of iron could also prove to be a problem. In fourth edition, most swords have a +3 proficiency bonus. This is highly desired to those who what to be able to hit their targets.
My solution, is to look toward other materials, and more primitive swords. To this end, obsidian is the main replacement for steal. Swords are not something that can be made out of rocks or glass easily, so older weapons, such as the Aztec macuahuitl are being adopted.
As for armor, scale is the easiest to explain away. A leviathan would make for a perfectly serviceable excuse for tough armor. Plate on the other hand, I can only think of perhaps monstrous crab shells.