Had the same problem on mine. Got one from A8 parts. Thought there is no demand for them and they will sell it cheep as chips just to shift it off. Turns out quite common problem and high demand. Don't recall price but it was reasonable( I think £15). Buddy of mine needed front springs so I just added to his order and saved on shipping costs. They have some on e-bay now:
http://cgi.ebay.co.uk/Audi-A8-D2-Coo...f#ht_996wt_902
Which is a bit high on price.
I have just updated my ETKA with latest updates including prices but have not had a chance to check and verify if they are correct. It shows dealers price £31.19 inc VAT. If it is correct then cheaper then A8 parts once You take postage into account.
Or You could get it from TPS cheaper if you can talk them into selliing it to general public or know somebody with trade account who could buy from them for you.