Yup. Many hatches can be locked in this way, in addition to one or two padlocks from the outside. Very rarely they may even have a torlift plug installed, which requires another (different) key to extract the plug.
Not seen any for sale, but they're fairly easy to make and the plans aren't the hardest to get ahold of either. There are multiple variations though. I know of at least two: the normal English key, and the Scottish one. There may be more, I'm not sure. And more variations of the torlift plugs/keys too.
Some pics of the two t-bar keys:
Std T-Key by
Gary Sutherland, on Flickr
Offset Scottish key by
Gary Sutherland, on Flickr
Again, it's not hard to find the plans if you want to make one yourself.