The Extras Christmas Special aired two Sundays ago. There didn't seem to be much hullaballoo about this. HBO is still airing it. Those with "It's not TV" can watch it Christmas Night at 7:30 ET, 6:30 CT, and Friday night at midnight ET, 11:00 pm CT. For the resourceful poor folk, I'm sure it can be found through other means.
By the way, it's really great. Gervais is has such a brutal comic mind. It's on full display in the special. The Clive Owen cameo is fantastically funny, and the ending is a pretty great coda to the series.