Sorry to hear it broke. So, are we talking 600EX or New 600EX? Short, medium of long cage? If you don't know, just post the part number, which should be stamped on the back of the parellogram. The cage attaching to the pivot or the other side or both? The reason I'm asking is because many Shimano derailleurs used cages with identical geometry. Expanding the selection of donor derailleurs will increase your odds of finding a replacement.