Enjoyed playing this game when we were in the US this year.

Mayfair have a photo of one on their website, but they also have a photo of a Rocky Backglass but it is not in stock.  Apart from the usual suppliers and posting wanted ads everywhere, might be worth contacting SS Billiards http://www.ssbilliards.com/sale.html if they have or can source one.

Good luck with your hunt.