The reason no one knows that Dunsparce evolves is because it never has until halfway into your X/Y play through. Here's how it goes....

Your entering your next town just looking for the next gym when you see a crowd of people around a park ranger or scientist explaining to the towns folk that miraculously a bunch of Dunsparce had evolved and flew off in the same direction. The informant leaves and everyone else is looking at each other puzzled. At that moment a young trainer runs across the screen screaming "No Dunsparce come back!". You walk that way and the trainer is just standing there crying, saying that he will never see his Dunsparce again and the before it disappeared it started glowing and it was the first evolution he had ever seen. Your character offers to help the poor young trainer and there a fun side quest full of mystery solving and bad guys begins.

Oh Dunsparce actually turned out to be an ancient pokemon who only evolve every so many years last time it happened was before the pokedex and all that mojo.

I was bored /vp/ and i had to get that story out of my head. If you have and cool ways that pokemon will be introduced give your creative writing a whirl!