Dear Geoff,
I have seen one of these come up on eBay. I will be more than happy to pass on some dimensions for you because it may be possible to make one. I have had a lot of help from J.R. setting up my old XB1. I am sure he might be able to help source one for you.
I would be interested in some pictures of an XA to add to my AR page
Best Wishes
Howard (Queensland)