If you are looking for high quality pre-made cables that output to a specific connector, generally RetroGamingCables or Retro Access are the best options.
If you are great at soldering, one option is to buy a console-specific video port from Console5 and replace the end of an Xbox 360 component cable with it. These are well shielded RCA cables that can carry RGBS plus audio left/right and you can adapt them to BNC with a balun.