Janice is right, ebay is a great place to buy bows. Etsy as well. Here are a few of the places I've bought bows from...

The best deal I found was this...you get to pick to pick two headbands and then 6 different bows to clip on to the headband. What I like is you can choose the style, size & color of the different clips!
Super Stretchy Cotton Infant/Baby Headband Set - Medium Bows - Infant/Baby Headbands - Cotton/Nylon

I bought a bunch of bows from here, I love the big oversized ones...
PinkBowtique : Baby Headbands, Boutique Hair Bows, Baby Bows, Baby Hair Bows & Little Girls Bows!

Warming the Heart - infant or baby headbands, baby bracelets, mothers bracelets, hair clips, baby shower gifts, flower girls, wedding accessories and special events

Cotton Headbands with Korker Bow - Band To Bow

eBay Store - Hair Bows: Headbands, Birthday Crowns, Pageant Socks

eBay Store - PrincessBowtique2you: Baby Bows: White Bling Baby Hair Bows Headband Hair Clip WOW

Etsy :: bluedandelion :: Blue Dandelion

Etsy :: lindsilea :: Livi & Co.

Hair Bows, How to Make Hair Bows Instructions~Baby

http://munchiemallow.com/index.php

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