I do not think the Low F (and high G) keys even exist.
The high bank reeds of an F accordion are as high as reeds go, and conversely, the low bank reeds of a G accordion are as low as could be.
But then, I've been proven to be wrong more than once :)
I may have imagined it, but I thought I had heard of a high G made not long ago. I had tried to order a set of high G from Binci by request, and they do not make them.