I had rejected our good local D&S leather supplier, as they do not do much whip work. In Dallas I have used and would recommend “Leather by Boots” for custom work. “Shades of Gray” does small work like adding D-rings and changing the length of straps.
I do agree that my best bet is finding a quality producer of whips and seeing about a custom order. I would appreciate any recommendations for this kind of craftsperson.