I actually got it from Japan thru e-bay (had to paid the premium ). The CTs over there have the shark fin antennas installed, whereas we only get a stick in the US. It was a direct fit: Get underneath the headliner from the trunk, remove the stock antenna, then install the new antenna. One thing though, the new antenna does not have the Satellite XM parts and the right wiring harness. So what I did is I kept the stock antenna and secure it inside the headliner. I then solder the stock antenna to the new antenna using a wire. I still get the same reception.
Yes, that's it. You can also find it in EBay just search for ZWA10. But keep in mind that it doesn't come with Sat. XM antenna and the wire harnes are different. If you want to go this route and wana keep Sat. XM, be prepared to do some mod like I do above.