Actually, I bought the Toyota accessory Sirius kit. Then I decided I didn't like the antenna being below the roof deck and got an exterior accessory antenna. The antenna I got is the one they sell on sirius.com. (Various people sell them on ebay, too... but I decided not to take that risk.) Then I got some color-matched spray paint from R&E Paint Supply:
http://www.repaintsupply.com/pd_barc..._clearcoat.cfm
I sprayed the thing myself, then mounted it on the roof.... The color matches pretty good. Just avoid bending the plastic parts after the paint is cured. Metal paints might be a problem for satellite reception, but mica is ok.

The antenna has magnets built into the bottom, and the wire-cover (for the few inches from the antenna to the edge of the roof) has double-stick molding tape. No drilling! I just run the wire around the edge of the window, to the trunk, and then inside (detailed routing is in my previous post.)

I'm sure XM web site sells similar antenna for their receiver. Or, the ones on ebay probably work just about as well... There's not much of a trick to reverse engineering an antenna or a connector. They're probably made in the same factory in china.

Ok I installed my Sirius antenna on the back dash. However, the red tape that comes with the kit is not strong enough to hold the cable down on the dash material. And the dash is not metal so the magnetized antenna itself won't stick without moving around when driving. I used one piece of Scotch tape to hold the cable down and it works. Never had a problem with reception. The black antenna doesn't match the color of the car well, so I didn't want to put it on the roof.