Closest I came come up with would be Power Tenon Cutters from Lee Valley. Principally used to cut round tenons on saplings for Rustic furniture and Chairs, Trellises, etc. There is a radius to the cut rather than a 45 degree chamfer, but that might look okay, too.
Try this link:
http://www.leevalley.com/garden/page.aspx?c=2&p=42299&cat=2,2180,41007
Can be used with a 1/2 " drill or hand brace.
