Thread about them is here:
http://forum.a8parts.co.uk/showthread.php?t=8020
Unfortunately, I can't help sourcing them.
I asked my friend in Germany who has access to german forums, so he can ask around. IMHO this is a true rarity.
I can suggest to set a 'followed search' on *German* eBay with the following string 'audi a8 d2 einstiegsleiste'. All good things come to those who wait.
Edit: My friend from Germany return to me and said no one is currently selling a set on german forums.