Ruger builds stuff in batches, I'm told they haven't built any single actions (except the Wranglers) in awhile. They might make more soon, or not. I don't know who schedules the runs of thisorthat, but whatever's making them the most money at that time is sure to get more attention. I haven't seen a new one in a fairly long time, so they might be getting ready to make another run of them, and Blackhawks, which I rarely see, either. I have a stainless Single Six that I'm very fond of, it's a real shooter.
I think they're concentrating too much on their fantastic plastic pistols, personally, but I'm old school and like steel and walnut, so I might be out of touch.
They are still listed on Ruger's website, so I assume they are still in the rotation and, eventually, in production. I kinda wish I had a copy of their manufacturing schedule, but so do all their competitors.