If everything else is still functional, the shaft is basically just a hollow tube with screw threading on either end. Most big box stores carry varying lengths of this type of tubing or you should be able to find some on the internet. You may not be able to find the exact same finish, but you should be able to get close. Worst case, buy three new tubes that are close and replace the broken one and the other two good ones so they all match. If one of the end connections that the tube screws into also broke, then it will be more difficult to come up with a solution.
I did a google search for "Pendant Stem Light Kit" and found a bunch of different options. Hope this helps.
Looking forward to seeing you guys next month.