Wireless keyboards and mice are not designed for nor do they have the range beyond a few feet. Because 99% of users have the keyboard and mouse next to the PC, a short distance is all that's needed. It's the simple fact that the power output of the devices are extremely low power.
In other words, there ain't no such animal that I've ever seen. All I can suggest is that you find a brand you like and contact them with your question.
I just installed a 37" flat panel Sony LCD Tv in the bedroom, I have attached a computer to it for streaming TV Shows and movies from the main server in the house. I am currently using a Microsoft wireless keyboard and mouse and they just dont cut it for the range from the TV to the bed.
Can anyone let me know what a decent brand of wireless Kboard and Mouse, that I can use with XP and probably with Vista if I ever get around to iunstalling it, range required is about 15-18 feet (4 or 5 metres) probably a bit less, but just want to cover myself!!