I bought all of mine from Schafer Hardwood Flooring out of Tecumseh a while back. There website forwards to some manufactured stuff now. Not sure if they still sell it, but it was really inexpensive and very well milled and finished.
Chelsea Plank Flooring down the street from me is/was twice as expensive and the people were kind of assholes... and neither their milling nor finish was as nice. But the guy lives in a giant mansion north of town almost to Stockbridge and has to get tax abatements to keep his employees so there is that.
It is really easy to do yourself, especially if you have a decent table saw, chop saw, compound miter saw, or radial arm saw.