The G100 was a remarkable instrument for a Hammond. Do a little hunting around the net and you'll find plenty of info and the full history. (include Hammond Grand 100 in your searches) It had, as you say, no drawbars but traditional stops. Trouble is, the normal TWG in a Hammond doesn't have sufficient harmonics to make accurate reeds, strings etc, so they added a second generator. Also had extra tremulants - 5 scanners (recipe for mechanical problems, maybe?) A flop? Financially, yes, as it was far too expensive to produce and only stayed in production for two years. Musically? The only one I ever played sounded good enough to me, but that was in the mid 70's and expectations were lower then! (No, it didn't sound like a B3!) As an instrument? It was big, very heavy and probably outdated by the time it was launched, with newer technologies just around the corner.
Hammond could never have made the G100 stick. They sensibly left church organs to others.
I wouldn't have bought one, I shudder at the thought of the maintenance costs! Will you ever find one being played? Who knows, but I somehow doubt it!
Best of luck with the search! Let us know what you find!