You can buy them from Convertibar as I just did when I installed my Convertibars but I also ordered new throttle and brake lines as well. I think the clutch was about $30.
You could check with MotionPro, too. That's who builds the cables for Convertibar and they'll build to suit your specs.
If you reroute your clutch cable out of the captive bracket located near the steering head where all the other lines run captively along the frame on the right side, you can get a couple inches extra distance with an OEM cable that may be suitable for your application.