The shells don't stay for long - if there isn't one in the workshop being dismantled at the moment then there isn't one at all. A8Parts is not like your run of the mill boneyard with a yard full of scrap - everything is carefully disassembled, the parts catalogued, and put on a shelf
Have you tried ebay? Someone here breaking two:
https://www.ebay.co.uk/itm/AUDI-A8-D...YAAOSw5VtaBsVR