Re: AR10 in 260
Yes, Armalite sells Their "AR10T" in .260 Remington. You can also get them from a variety of places such as JP Enterprises, GAP etc chambered in 260.
I have both a JP complete rifle (DPMS platform) and an upper built by Scott Mesesha on an Armalite platform. They both shoot lights out and function flawlessly. Great cartridge for the AR-10 in my experience.