Thanks Phil, I asked at my local Lowes for non treated 4x4 several years ago and they said they have never seen it. I guess I need to ask can you order it. I was also looking for non treated decking boards, I wonder if they can order those also.
I usually mill my own. This summer I dropped a large pine for my neighbor and milled a stack of true 6x6s and 6/4 kick boards from 8'-14' long. Any local sawmill will probably cut them for you.