They are available but it takes a lot of time and money to do it the way this one was done. Rebarreling the Ruger receiver isn't so bad but welding the stainless tube on the rear of it with precision is more difficult. The welding is necessary to bring the overall length to the unshortenable, legal minimum. All the other parts, and there is a variety from which to choose, including the woodwork, are easy to fabricate.
I've been talking to a popular Ruger aftermarket manufacturer about making the receiver long enough to begin with so the welding can be avoided. This, If he will do it, will bring the price way down. The idea, of course, is for the Markll owner to be able to remove the grip frame from his pistol and insert it in the rifle receiver.
Are they salable? Let me know what you think.