They are an extremely rare find now, you can try calling the Pantera vendors and see if they have any used parts, I'd also reach out to Mike Mayberry, it's surprising what he has, but expect to pay close to $1,000 for it, if you can find one. Otherwise it's keep scouring all the forums and FB marketplace and hope one comes up at some point.
I think I have a the 37A lid piece somewhere as I converted to an aero style cap. That maybe another way to go, just cut a hole in your existing gill and mount an aero cap. You'll also need to cut the holes through the rear panel for the hose.