I have seen one on a dog at a show but never thought to ask where from. I have been googling combination martingale collars but am finding either adjustable ones or just normal ones without the D ring? Any ideas on other words to try googling?
Here's a picture of an all leather one - if this is what you want you could try searching for the listing company
I had my show lead (normal rolled leather slip lead) hand made so I'm sure it's possible that someone could make one for you if the style you want isn't commercially available. Good luck