It says to go to a lumber mill, but I've been to 4 already, and non have the option to sell me logs? Is there some place where I have to cut down trees or something? I can't continue Hearthfire until I find these sawn logs.

You are supposed to be able to buy them from the guys who actually run the mills. Such as hod from the first town. If he doesn't, you can buy them from your steward.

I must have a bug then, because none of the people I talked to have an option to sell me logs. How do I get a Stewart if my house is incomplete? Or are they just a follower type person I can run into regardless of whether or not I have a house? And if so, where are they?

You use your already available followers. I used lydia

Hod in Riverwood will sell you logs.

yes hod in riverwood will sell you logs, it is in fact the only dialouge option i have from him

He was the first one I went too, with Riverwood being one of the few mills I know of, he wouldn't sell me any, so I went to Temba in Iverstead, and it was a no go there either. After than I just started fast traveling to random mills and talking with everyone.

Deleting Hearthfire, and reloading a save prior to Hearthfire fixed the problem, Hod will now sell me logs.