Welcome to the forums Matt!
As far I know there are no ring kits available at the moment. There are other really good options though (just as accurate as the ring). At the moment your best bet is to either make or buy a linkage. They can be made with some basic tools and a little know-how, or you can purchase laser cut kits. Dlang makes a kit that mounts on the top of the sled and I make a laser cut kit that mounts around the router.
You can find much more information (and links) here: Linkage kits are now available! 🎉
Let me know if you have any other questions!
-Logan