Looks like Microsoft has a few units of the Xbox One Day One Edition left, and they've now been made available on the publisher's official Ebay store, as seen in the picture below.

If you're interested in getting your hands on one of those sleek black boxes and on the achievement that comes with them, you can find them here. You may want to hurry though, as they're unlikely to last long and the listing clearly mentions a "limited quantity available."

Update: the listing has been taken down by Microsoft with the following reason: "This listing was ended by the seller because there was an error in the listing." Only two units were sold before the removal.