The wing nuts can be purchased directly from AMK Products out of Winchester, VA. This is the place that provides the hardware to many of the vendors. They do have a $30 minimum order, but it does not take much to put together an order as they have so many pieces once you start to looking at their inventory.
If you are really wanting 100% correct wing nuts, you will need to find originals. The reproductions are close and most people do not know what to look for, but the originals do not have the radius that the reproductions have.