You might have a little luck with the search facility, though it's a bit hit and miss. Someone, it might have been Dunbarharmlin, has made them and I think walnut is a popular choice for stocks.
Think I even recall seeing a link to a shooting forum with some folks there that had made their own
Post some before and after pics, please, if you decide to go down this route.
Why do you want to make your own? Is it just an interesting project, or for a specific reason? My dad made one for his air rifle, many years ago, and made the butt a bit longer, so he could use it more comfortably.