http://www.scosche.com/scosche.caraudio.new/?applicationGuideID=13752
&make=HONDA&year=2006&model=CIVIC+W/INTEGRATED+RADIO+(Gray+Dash)
the two companies other than getting the OEM navi panel are Scosche and Metra.
the link for the scosche kit is above, I personally have a double din pioneer unit in my 06 civic lx (06 and up = 8th gen civic should be the same), i ordered the OEM navi panel from my local dealership for about 30$ and got a trim ring for it fabricated from a local car audio shop for 10$
If your concerned with your steering wheel audio controls not working with a aftermarket HU, PAC audio i believe makes a adaptor that will make your steering wheel controls works wit a aftermarket HU
http://www.pac-audio.com/
Hope this info helps, pm if you need any more help or for more ?'s