All servers of the competition have a redirection. If you have not the map, you can download the files directly in the game.
But if you have not a good connexion, you can download this package for prepare the competition :http://gfaro2.fr/cup/2015-riflecup/Files-client-riflecup.rar
The installation is very simply.
Download the package.
Extract it in :
Your hard disk(C in default):\Program Files (x86)\Steam\SteamApps\common\Red Orchestra 2\ROGame