Yes, Hellblitz, you would need to purchase a new copy of World of Warcraft in order to acquire a new retail Authentication Key. It is also possible to acquire a Trial Key by using the Recruit-A-Friend Program (http://www.worldofwarcraft.com/account/recruit-a-friend.html?). The Trial Key can be used to activate a 10-day free Trial Account, which can be upgraded to full version at any time by visiting the Account Management Page and choosing the "Upgrade Online Right Now!" option.
However, with that said, it may still be possible to recover your old account. In order to do so, please contact our Billing and Account Services Department by phone, at 1-800-592-5499 (Mon-Fri, 9am-6pm PDT). I hope this helps, Hellblitz. Good luck. :)
Coreiel broke 25% of my heart. </3