Need a plastic orb big enough to fit a head inside!

Hey there, I'm trying to build a space costume with a light up orb as a head (completely or mostly round), and have run into a dead end! It has to fit a head inside of it, thusly nothing has come up. If you can help out, I'd really appreciate it.

Thanks! Ex: http://cache3.asset-cache.net/gc/85731545-young-man-holding-orb-of-light-in-front-of-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=iVCLEX4xtEUHO4yYTiiAEWbe6GzikaknzuqIjgHZZNvXHkuLOLx9eTPKFWqNk%2BD7