I knew as I was typing that, that someone would find one and "prove" me wrong. But I'm sure you're aware of the fact that there are considerably more horizontal shaft edgers than vertical ones. I've lived in the Washington D.C. suburbs almost 60 years, and worked on more than my fair share of equipment(considering that I don't do it professionally), and I stand by my statement, but add the caveat, I've never seen one "in the wild".
And I'd add that it's not as efficient as using a horizontal shaft motor. Any time you make a turn in power, be it a shaft driving a differential, or a twist of a V-belt, there is a loss of power. This is why shaft driven motorcycles have never been able to compete with chain driven bikes in racing. Gearing may make up for some power loss, but speed is compromised.
The last thing I wanted was to hijack a thread.