A close matching option for our OEM 9/16"-18 closed end ball seat lug nuts that I have found is to get a set of Ball seat lug nuts on ebay (designed for Porsche)
http://www.ebay.com/itm/20-Premium-Chrome-Closed-Ball-Seat-Lug-Nuts-For-OEM-Wheels-M14x1-5-1-26-Tall-/400954828631 ($31.00 W/ free shipping for 20)
These lug nuts have a 14 mm thread but I have found that the smaller 14mm thread will re-tap nicely to our larger 9/16"-18...I have contacted seller to see if these lug nuts are available as blanks so they could be threaded to either right or left hand thread but are not available at this time....Anyway, on my model 40 I only needed to change one wheel over to have all wheels with right hand lugs...

This is a picture shows a few re-threaded lug nuts, the one at upper left is a worn original...

Where Are You From? Leavenworth, WA / Yuma, AZ

Do You own a car built by Durant? Yes