ok first upload your sound files that you wish to use to the following directory;
Then you will need to add the files to the random_winner_sounds.txt file this is located in
cstrike/cfg/gungame5/random_winner_sounds.txt
And enter the sounds as per the following as an example;
gungame/song1.mp3
gungame/song2.mp3
gungame/song3.mp3
Replace the song1, song2 and song3 with the file name that you uploaded to the folder