It may not really be your style, but almost every nice hankerchief I have was found in a thrift shop or consignment store. It does take a little bit of luck but I've picked beautiful delicate hand embroidered hankies or hankies trimmed with hand tatted lace of a quality that really isn't available anymore. Plus, they are usually incredibly inexpensive. Although this could be pretty time consuming with a wedding coming up!

The other place to try is bridal shops. They often carry a lot of bridal and mother-of-the bride accessories.