For convertible top parts suppliers, please refer to the Convertible Top page.
ETKA software, made by LexCom GmbH, is/was used by VW/Audi dealerships to look up parts and their respective part numbers and prices; ETKA provides illustrations for virtually all parts and accessories of all VWs. This software is available to the public and is available through VW dealers at a hefty cost. eBay sellers often have ETKA CDs for sale, but buyer beware: these CDs are really bootleg copies of the actual software and are often not for North American models (majority are sold from European locales) and require a certain screen resolution and may require additional software files to run properly; be sure the CD will work on your computer prior to purchasing.
If you'd rather not buy ETKA, you can always visit the following free-to-use sites:
7zap (ad supported; not mobile-friendly)