Sometimes it's funny what you find on the internet when you are
not looking for it! After some research on aftermarket center stands for the XTZ I decided on the genuine Yamaha item, and it has worked well for me.
However I have discovered the following company
http://www.lexs.nl/ who fabricate a centerstand for the XT660Z, XT600, XT660R, XTZ750. The price is above par, however I would have gone for this option in materials (stainless steel) if I had discovered it earlier.