I only knew to look on Tonton Velo. What other fora are you looking at? I speak French fluently so I'm looking at joining one or two as time permits.

Rare birds are good. The authenticity police won't be after me for putting it on a '46 or '47 Herse, because they'll have never heard of it! The one I ought to have should be brass, or wartime black painted steel, but this can be a placeholder.

Finally, I have a working hypothesis about this. No, [MENTION=45088]nlerner[/MENTION], it does not have to do with the co2 inflator thread I regrettably posted on the other day.
GiNA is probably a bike shop, who paid to have a run of pumps with their logo on them, done by some major aluminum manufacturer (the mysterious MG perhaps). This was done by at least one other manufacturer, M. YVARS, as seen in this thread. Other (newer?) GiNA pumps on French Ebay are definitely rebranded Zefal. Smart advertising! You make sure it's the cheapest pump in your shop, and customers will pay you for the privilege to carry around your logo! Here we are 70 years later, wanting to know more about GiNA. So, I bet that's what's going on.

Searching for Établissements GiNA gives me nothing, and there's no case-sensitive internet search, so I can't try that. Monobloc pumps were a Zefal thing, and this one really looks a whole lot like the venerable Solibloc (seems similar length too), albeit with a different (older?) plastic cap (with the MG marking) and a different handle. But I'm somewhat content with this theory. Of course, I welcome criticism and opinions!