Bucanero make those shafts.
https://www.diveshop.gr/index.php/137.html
It is easier to make the floppers lie flat on the shaft with them offset on two pivot pins as the flopper pairs don’t nest in each other as they do on a single pivot pin. Single pivot double floppers originated with detachable screw tip shafts, both floppers open up to engage on the fish provided the shaft goes right through it like a T bar.