i would think you could also take a safari-style hat (or a straw hat of similar shape) and a strip of gauzy netting from the fabric store and make your own. stitch or glue the netting to the brim of the hat, then run a seam along the other edge (that would go around your neck) and put a cord in so you can cinch it up a bit.
or you could add a bit of wire or thin plasic tubing to make it a bit firmer like this:
i know that technically the firmer screen is safer in *actual* beekeeping since it keeps the screen (and therefore any aggressive bees) from bumping against your face, but for a costume, you could easily get away with it. =]
such a cute idea!!