I guess you are referring to the cyclinder in the brake drum. Im not to sure. You would need to find out if it shares the same part number. You can get them resleeved if your original is stuffed.
What master cyclinder
do you have up front? A single, duel or a T50-12? Upgrade to a T50-12 for better stopping power and safety.
You can buy parts from here. http://www.kainzmaier.de/index.php/en/