I've now added the third skid gear to the North American Aviation X-15 3D Model. It was flown on X-15-1 for it's last 12 flights and on X-15-3 for it's last 14 flights. This is a very approximate 3D model.
There is a reason why it's a very approximate 3D model, I've only got two images to work with. One image is from a book titled "Hypersonic: The Story of the North American X-15" by Dennis R. Jenkins & Tony R. Landis. The other image is from an accompanying book called "X-15 Photo Scrapbook" by the same authors. However I don't have the second book, but luckily found an image from the book.
I've asked Santa/Father Christmas for this book, but the elves haven't reprinted this book in years. If you have this book and have no requirement for it, I would be happy to purchase it from you.
This is one of the images: