The CP of pokemon you encounter will go up as your level goes up. I'm at level 17 and so now i'm encountering a lot more 300-500 CP pokemon. Occasionally I might run into something 700+. So just keep catching pokemon, hatching eggs and visiting pokestops to level up and you'll be running into...
I was at work when this turned up nearby. Fortunately I work at a game store meaning all the customers are also nerds and one of them went to get it for me.