Try caraudiocentre.co.uk, caraudiodirect.com, caraudiodiscount.com, hendoncarstereo.co.uk or denison.com.
(Told you I'd done some looking.)
The fasia plate is about a tenner, and you'll need a wiring harness adapter. MAKE SURE YOU GET THE ONE FOR THE INFINITY SYSTEM they're different to standard.
To remove the stereo grab the center console by the bottom corners and pull! It's as easy as that. There are Two hex head screws holding the stereo in place (10mm I think). Whip um out unplug the head unit from the loom, plug in your adapter, plug other end into Sony head unit stick it all back together and ENYOY!!
P.S. make sure you mount the Sony in the fasia plate the right way up (like I didn't)- the wider section goes at the top. There's enough room to feed the wire for the Denison cradle between the centre console fasia and the dash.
The whole job should take about 20 mins.