The Rzeppa joints on these shafts are not serviceable. Your options are a new factory shaft, a used factory shaft from someone that upgraded, or going with an aftermarket double cardan shaft.
You can sometimes find free, or very inexpensive, used shafts, but as noted above, it will be a temporary fix. Due to the lifted angles, it will just keep happening. Aftermarket double cardan shafts are a better option, as they handle the angles better. They have their own issues with the caster/pinion angles, though. So do a little research to see what your best option is..