My daughters are very girly girls and love to wear bows and headbands. I know a few SAHMs who make bows and sell them, and they will even take custom orders if you are trying to match a certain color or style. Try googling hairbows and then the name of your city, and see what comes up. You can also look at farmer's markets or little boutiques. In our town there is even a whole store dedicated to hairbows in the mall! No kidding. However, they are not cheap. The inexpensive small ones are $2-3, and it just goes up from there.
May I suggest as well that once you start in with buying hairbows, get a length of ribbon you can hang on the wall, so you have somewhere to store the bows without crushing them in a drawer.