There is one pictured in this listing. They seem absurdly rare. I'd go for this deal, except I don't want and FCM, I want an FCM2 like yours...

The holder attaches to the accessory rail of the rear standard, and clamps the holder across its narrower dimension, side to side, just like you'd hold it in your hand. The knob loosens both the clamps grip on the meter, and the clamps attachment to the camera.