This unit was not available in Australia so I bought one in the U.S. That meant it came with the U.S. map database installed and only had capital city locations for here. I was unable to find any download site for maps so, like you, would be interested if there are any.
I eventually purchased the Garmin MapSource WorldMap CD on the Net and install the maps from that. When away from home on very long trips, I use a laptop to add/delete maps as required. BTW, the maps for this neck of the woods are in serious need of an update. On a recent trip to the centre of the country, I found that occasionally the map was up to 15 (FIFTEEN!) kilometres in error and at other times it was spot on. Usually around major populated areas (like the east coast) and in the major cities the map is pretty accurate. It is very handy for orientation though and the tracklog great for finding your way back in the bush, or in your case, the desert!