BNC is very old technology, it is used mostly by CCTV networks also some test equipments in electronics labs. You can get BNC to RCA Connector adapters.
Almost all modern Displays & Computers use VGA or DVI connectors.
You can also get VGA Matrix making it easy to connect it to any computer output and then distribute signal via existing BNC cables to TVs.
Most people would just use multi-output Video cards like MATROX to drive multi displays or use splitters if same image is over multi location.
MATROX also do Graphics card that have 8x Mini-DP outputs and can run up to 16x Screens if 2x cards are used on single computer.
VGA to BNC means 5x BNC connectors just to convert RGB. 1.Red 2.Green 3.Blue 4.HSync 5.VSync
