Does anyone know anything about buying extra pieces? I want to buy the the whole elf faction for my game. Troops, Resource Dial, and Order Cards.

You can try contacting their customer support, but from past experience FFG doesn't typically sell parts individually; you'd have to buy the whole game.

just curious... why just the elf faction?

Maybe he wants to try an elves vs. elves game or something like that.

We want to play a five player game so I was going to paint them a different color.

I would strongly recommend you to buy another copy then and take a fifth of the other stuff as well - heroes, tactic cards, and so on, since all the components are balanced for four. And what about the hex tiles? Don't think it'll work this way.