Under "about Avis" on their website, it lists
6 Sylvan Way
Parsippany, NJ 07054
(973) 496-3500
as Avis World Headquarters. About 6 months ago when I needed an address, the only thing listed was a customer service address in Tulsa, OK. I wrote there and got no response. When I contacted the Better Business Bureau of Tulsa, they were able to get a response. Now that the Tulsa address is gone, I guess I'd send it to the NJ address. Good Luck!