If it is a removable cable, then you should be able to pick one up at a computer shop or office supply superstore. Usually, removable cables are double-male 15 pin VGA. Be sure and get a good shielded cable - some of the real cheap ones work very poorly.
If it's not a removable cable (hard wired to the monitor), then it's really not a do-it-yourself repair and should be sent to a repair shop.