Not sure you'll get one as the S-Video connection keeps the all-important black and white (Y) information separate, and combines the colour difference signals into a single colour signal (C). Instead of three separate signals going to a display device, there are now two separate signals. A composite RCA connection blends all signals into one, dirty stream.
Unless of course you want to send the signal from an S-Video output to a composite input, then this is possible.