Here's a site from which you can order a new dvd:
Toyota Parts and Accessories Factory online parts catalog cheap Wholesale Prices
Gotta warn you: nav kits don't change much from year to year, so you won't be gaining a lot getting a new dvd, the info on the new dvd is still a couple of years from being current, and you might have trouble with your system making the change.
When I upgraded to a new dvd for my wife's '05 Avalon, the new disk effectively crapped in the player and the nav system never worked properly again. Your results may vary, but if I had it to do over, I would leave it alone.