You can find them lots of places I got an under armer one from sports authority that is really great and can last a few years but my school year only has a month left where do you live/ go to school. :)
If you go to the pink section at Victoria's secret you are sure to find some cute backpacks. The bags are durable and pricey. You can also checkout other stores like Wal-Mart, Zumiez, Pac Sun or Target.