VAG spares
 

If i need spares for my A8, do i have to go to a Audi dealers or can i get them through any VAG parts department?
Might seem a daft question, but i know VW don't let you buy VW Commercial spares from a VW car parts dept, you have to go to the local VW van centre - so do they also make you buy Audi spares from Audi parts dept?

Obviously some spares are generic so would be obtainable from VW, but for parts which are fitted only to the A8, is it Audi only?