Hello Karen,
I think there is a danger of over complicating this. If you are buying secondhand, then I cannot really see a great advantage in part numbers for panels. Simply take photos of the parts on the good side and ask potential sellers to e-mail exchange photos with you for what they have.
If you really do want to have the part numbers then I would be ringing an Audi dealer,armed with the registration and VIN numbers, and asking for prices and part numbers.
Kind regards,
Gareth.