Purchase - Historic Enterprises sells historically accurate costumes for men and women. Each item in their catalog actually comes with an accuracy rating! Not the cheapest, but well researched and, from what I've heard, well constructed. This long tunic/gown (depending on whether it's worn by a man or woman) is $100 in linen, or is available in wool for $110. If that's too expensive for you, there's also a handy pattern diagram on the catalog page.