Depending on how bad you broke it, it could be plastic welded. Other options would be to glue it back together with an adhesive that can withstand brake fluid and pressure, maybe a JB Weld product. I'm not sure if there is a cross reference to a different master cylinder or not. Two worst case scenarios, you buy a new one and have extra parts to rebuild. Or 2nd you go in to a dealership look at the other bike find one that matches and order it. There are a couple of dealers that you could call that know their Buell's. They could help you. St. Paul Harley comes to mind.