Is there a source, other than a dealer, to get the rear hub nuts for a 2006 XJR? The ones I've found online only go up to 2003. Are they the same?

 

I don't think so, but they will be standard nuts to a particular steel specification, I'm sure, and not made specially for the car. The same nut is probably used on the S-type and XK cars, and probably the XF. I would enquire of one or two of the reputable Jaguar specialist spares suppliers on the internet. They'll probably sell you the Jaguar part !