Not often they come up and when they do its definately a PROJECT!!
If you find one.. drop me a line as nearly all have the armatures that drop the balls in the BG down broken... and this leads to missing balls.
Ive just made a vector file of the armatures and will be having these cut in 1mm aluminium. I pay for an hours cutting so ill have plenty spare.
The balls will also be made and im still trying to work out a way to get the artwork on these so they look original. There were some repros made a few years back that i have a set of but they are nothing like the originals.
Good luck.. is an awesome game