I looked if there are still new DVD-RAM discs available to buy here in germany. There are, but only in some online shops. People in other parts of the world might have more choices.
If no DVD-RAM media are available, DVD-RW media could be used as an alternative. The workflow is not as straightforward as with DVD-RAM though:
1. Copy the whole disc content (repositories) to the computer
2. Update repositories
3. Burn all the content (repositories) onto disc