If you don't have time, you must buy the map at a local reseller, because even directly with Garmin lasts download several hours .
Or use torrent, where you get the download in one part.
The other way is to use a download manager like JDownloader, then this tool downloads for you all parts automaticly. With this links JDownloader works properly:
http://www.navitotal.com/showthread.php?10645-City-Navigator-Europe-NT-2013.20&p=88892#post88892
By the way: ***.gmap is not only one file, it's a folder with hundreds of subfolders and files