Hi Nick
I have also been looking for a solution to this.
One option would seem to be the new CB subs component which would subscribe CB suscribers to a VM group.
I also recently found the following new "Virtual Vendor Extension" on the Joomla extensions site.
extensions.joomla.org/extensions/extension-specific/virtuemart-extensions/8239
. The developers homepage can be found athttp://www.nordmograph.com/downloads/doc_details/40-vmvendor-suite-for-community-builder.html
The combination of the above two items looks like what you are looking for.
I am also wanting to integrate the two systems of VM and CB together and would value your input and comments once you have evaluated my suggestions above.
I am trying to figure out which login system to use as the "master". It seems to me that perhaps using CB as the master would work best as long as it transfers the information appropriately to the other components such as VM.
I hope my suggestion is of use to you and look forward to your reply and comments.
Regards
Greg Eales
Port Elizabeth, South Africa