Another source is Becker Autosound. They are the representative for the Harmon Becker radios in the US Crossfires. You will need, in addition to the radio, the GPS antenna, the two connection wires you mentioned and the radio antenna adapter to connect the stock FM antenna to the plug on the radio. I just spoke with Ed, a gentlelman at Becker yesterday and ordered the parts for my upgrade on a 2005 roadster. They are very easy to deal with on the phone. Here is the link with phone numbers.
Becker Autosound Website
Good luck