you sure its not 3.5mm? Try a mobile phone headset plug and see if that fits which would confirm. I have a mix of 3.5mm and phono on the cameras I have which is a pain. There's plenty of add-on mics out there (amazon, ebay etc) of varying quality, some with adjustable gain and others AGC but few rated for outdoor use so what you choose will depend on your requirement. Also note the audio quality will depend on your camera's abilities, some are good others less so.
This mic reviews well and I can confirm it gives good audio, tho I have other cheaper ones that do pretty well too
Bullet Mic Review
Don't forget that you will need to enable audio at the camera (via its own GUI) as well as at the back end.
