I got mine off of eBay, just look for heated seat kit and find the one you like for your setup. There are many, many out there with different configurations and switches. Some have on-off settings, some are hi-lo-off, this one has a 1-5 dial setting. I did the hi-low-off in my old TJ and sometimes hi was just way too much so I decided I wanted some more settings this time around. This morning I started out on 5 but after a few minutes, it was too much, I dropped it down to 3 for the rest of my commute.
Here is the specific one I purchased.