just search ebay for nissan homelink mirror. pretty much any of them will work, (ones without the compass) I happened to find one from a Maxima that was like 30 bucks. There's one for 49 out there now. Then pick up one of these:
Gentex Auto-Dimming HomeLink Mirror Wire Harness Kit : eBay Motors (item 140384080452 end time Mar-18-10 19:13:01 PDT)
And then hit up Courtesy Nissan for the little plastic cover for the wires.
COVER-INSIDE MIRROR - 370Z (Z34) 2009+ :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com
Altogether it cost me around 70 bucks for a homelink mirror, sure beats what Nissan charges for the kit.