Why don't you get a USB GPS receiver and run a software solution?
I use one of these:
Wrong country I know but I got it bundled with Odyssey Navigator software from here (prices in AUD):
I fitted this under the plastic cowling where the windscreen wipers are. It works a treat. I had to daisy chain it via a Hub as the Car PC is behind my back seat and the cable length was too long for USB to work without a hub. I cut the USB connector off and fed the cable through the firewall and resoldered the connector back on.
Details in my buildup, see link below.