I haven't been in an electronics store in a long time, but they're readily available online, including at RadioShack's website, so I doubt you'll have any trouble.
I hope you're saving up for a new system, as S cable to HDMI connections are surprising expensive, meaning that if either your TV or your video player (VCR? first-generation DVD?) goes, you might just want to replace them both. But hey, I admire someone who doesn't treat major electronics as if they're disposable. Keep them out of the landfill as long as possible!