I have a couple Sony KV25XBR with a 34 pin connector on the back. According to this guy:
http://www.inwap.com/inwap/chez/kv25xbr.txt
pin 21 is the digital/analog selector for RGB in, and it has various sync options.
Is that what you're after? (I know it's not a trio of nicely labeled BNC connectors...) I've never set mine up that way.
This was a nice set in its day.
Chip