USA Network plays NCIS from 5-8 every weekday and usually has one day a week that has an over 12-hour marathon of it (currently it's Wednesdays). I know here it is channel 24, but I don't know what USA would be where you are at. Good luck.
USA Network, ION Television (local channel 30), and CBS all rerun episodes. If you have DVR you can search for the show and all channels will come up...really easy to set it to record. I caught up with the last 3 seasons in a month that way.
Here are the websites I use:
www.cbs.com - you can usually find them on here
www.watchncisonline.net - you can only watch like 74 minutes at a time then you have to wait 1 hr before watching more but it has ALL episodes Season 1-6 and you don't have to download them.