The full NSDB can be extracted from the IPS MC update.
Download the corresponding IPS MC update.
Unzip the file using WinZip.
There is a nsdb_html.tar file that you can extract to your local PC or a local web server on your closed network.
We had to replace the full NSDB on the sensors because of disk space issues. The full NSDB is fairly large (close to 90MB), and is using up too much space on the compact flash based sensors with only 512MB of disk space. The NSDB was so large that it was preventing the download of the 5.0(1) upgrade so 4.1 sensors could not be upgraded to 5.0(1). In S206 the full NSDB on the sensors is replaced with link to the corresponding pages on cisco.com to free up disk space needed for upgrades.
The full NSDB, however, will continue to be delivered as part of the IPS MC upgrades.
You can download the IPS MC signature update and extract the full NSDB even if you don't have IPS MC. You can just use winzip to do the extraction.