Ask and you shall receive. I'm not sure I totally agree with their description, but it does work.
Worlds Smallest Longest Range 2.4ghz Radio Remote Control Wireless RC Camera
Here it is mounted on a flatcar. I actually want to mount it in a locomotive at some point. It runs on a 9V battery, but it's somewhat of a current hog, so you really want to power it from track voltage. I believe it draws about 100ma, so it'll suck a 9V battery down in a few hours.