Apple discontinued iDVD and iWeb some time before Lion was introduced. Apple is going in the direction of sharing via the cloud hence the introcution of iCloud and the demise of MobileMe.
You can obtain iDVD by purchasing the iLIfe 09 or 11 disk from a 3rd party retailer like Amazon.com.
However, If you do purchase an iLife disc remember that the iLife 11 disc only provides iDVD 5-7 themes. The Software Update no longer installs the earlier themes nor do any of the iDVD 7 updaters available. from the Apple Downloads website contain them
Currently the only sure fire way to get all themes is to start with the iLife 09 disc:
This shows the iDVD contents in the iLife 09 disc via Pacifist:
You then can upgrade from iDVD 7.0.3 to iDVD 7.1.2 via the updaters at the Apple Downloads webpage.