What's up man, I can help you out here. The sound files are a little complicated, don't go download them, as it's just gonna be a large download and I can't find a place where you can find them ALL.
The place you can find them is the Riot Games folder on your HDD. There is gonna be one main place you can find them. You will have to download a couple programs to be able to play them. You also may have to find some audio converter files online to get the files in the format you want them to be.
Here it is, now this is gonna be where all the sounds are, I'm pretty sure anyway
C:\Riot Games\League of Legends\RADS\projects\lol_game_client_en_us\managedfiles
Hope this helped, let me know if this doesn't include all the files you need, and I'll do some more digging later and edit this answer.
ALSO BE AWARE there are MANY fake conversion files out there, there is a high risk of getting a virus. Just be careful when you are searching for those. Don't just hit the first 'download' button you see.