Alright.
To expand on what Matte had to say.. Wireless video cameras would suck! the bandwidth required for this would be higher than what technology is out (AFAIK). If there was something that you found, it would be compressing your video which you probably would not really want.
Why do you want these to be wireless? You can just run two video lines to the stage, which in most cases, would be MUCH easier than the configuration time that would go into a wireless setup (assuming there is such a thing!)
Give more of an idea of why you want this; we could probably point out a better solution.
Enjoy.