The DMC’s vnets service has been retired. But not to worry, virtual networks are alive and well.
To browse virtual networks the DMC’s Metadata Aggregator (MDA) is the best choice:
http://ds.iris.edu/mda/#vnetlist
For programmatic access to virtual networks, both virtual network definitions and resolved listings are available from the DMC’s virtual network web service:
http://service.iris.edu/irisws/virtualnetwork/1/