Hi Dan,

Sorry to hear of your tale of woe. I was about to give some encouragement by telling you about a similar thing which happened to me when the balls dropped out of my Z axis profile bearing when it moved past the end of the rail during assembly (!). I can sympathise with the tap-tap-tap sound followed by crapping yourself. Anyway, they were actual fairly easy to get back in on the linear bearing.

This may not help, but my ballnuts (of different design, but perhaps could be made to work?) were around £55 from MotionControlProducts.