Going to be a bit tough to find; I know Sony don't make one. It's a reasonably common jack, though.
You'll see it described as an AV/R or A/V-R plug, sometimes colloquially as a '10-pin D' plug due to its shape and terminals; look above the HDMI jack on your camera. The hard part will be finding a male-to-female extender & a quick Google didn't bring anything up
Another solution might be to get a LANC adaptor cable (AV-R to LANC) which may also extend your remote control options, as LANC is a very common video remote interface and there are a lot of LANC controllers around. The best thing in this case would be to take the camera to a quality (ideally professional) camera store and try out some basic LANC controllers in conjunction with an adaptor cable and see what works.