I took most of the random encounters from fallout 3, and tweaked them to fit the rules for the 2d20 system.
Fallout 2d20 Random Encounters - Google Doc
Note, just like Fallout 3, your players can run into an encounter that is way above their level, so you might want to give them a chance to avoid their encounters. (Sam Warrick ended a lot of my YOLO playthroughs.)
