This is the one I'm looking for online.
This site is out of china. I tried to purchase online, but when you "add to basket" your adding to an inquiry basket and they want a bunch of info just to send you info.
A guy on another forum site said he found this one at a farm supply store.
Hot Water Float Valve
The gravity thing is a great idea. I may try that.
I was thinking this evening that a 90degree elbow adapter could be used to secure the toilet tank float to the side, rather than the bottom of the tank.