The overwhelming majority of cable-activated disc brakes are single-piston designs, including the exorbitantly expensive Paul Klampers. On most of them, you have to manually adjust for pad wear; it's not a big deal, but I find the whole design kind of finicky. TRP Spyke brakes are cable-activated but have two pistons; they're pretty great. Alternately, you can get hybrid brakes that use a cable to activate hydraulics in the caliper (like Yokozuna or TRP HY/RD); the pistons accommodate for pad wear. They can be expensive, but still less than some full hydro brakes.