Nearly every motorcycle mfr makes 1:2 throttle cables with Mikuni ends. The other end is a cyl of lead, sometimes a sphere of lead. There is bulge in the middle of the cable about 1-3 feet from the carbs that is the 1:2 coupling.
Yamaha 650? Honda 350? Kawasaki 400 (twin?), there are a million of them. Find out how long you need, then go to your local motorcycle junkyard.