You cant find a good .wad file with a good sky. If your going for a cartoon like game i recommend that instead of the tectures you build clouds in MED. Then make a sky blue texture, Also you could either model your own sun or download one.

-You can find some textures, and models here??
http://au.conitec.net/

-Im sorry, but thats the most help i can give at the moment.

-Wh1t3 W1d0w