HDMI to S-Video converters or the other way around. S-Video (SVHS) is an analogue signal and HDMI a digital, so an electronic conversion is needed.
Please note that the direction should match the purpose, i.e. whether, for example, you want to send an HDMI signal into a device with S-Video, or an S-Video signal into a TV with HDMI.
As the S-Video standard is rarely up to modern picture quality standards, it is often advantageous to invest in newer electronics, e.g. a new Blu-ray player instead of an old DVD one, if the TV only has an HDMI connection.