I think Derek Lockwood has king size bargellos. If he doesn't I'm quite sure he can add to one to make it king size.
http://www.lockwoodquilts.com
Just be prepared for the yardage. Typical king size quilt will use about 10 yards total of fabric. A bargello king size may take up to 20 yards total of fabric. So be prepared for the "sticker shock"