NBU agent for VCS

Where would I find the VCS NBU agent package and documentation.  Normally you can find an agent at https://sort.symantec.com/agents or in the bundled agents guide, but I cannot find NBU agent in either of these locations.

I am planning to upgrade an NBU (master) VCS cluster from 5.1 to 6.1 so wanted to look at VCS 5.1 and 6.1 agent docs and also obtain the 6.1 VCS agent package

Mike