Wha...??!! That's not good. Well, I think the 2020 kit includes both diaphragms... if he still sells that kit, you could buy that and get the diaphragm you need (and toss the other one). If he doesn't sell any diaphragm kits, shoot, that is depressing news.

Otherwise yes, if someone could find a pod from a different chassis that uses the same diaphragm, you could buy one of those pods and swipe the diaphragm from it.

I believe another option is to buy one of the dual-diaphragm pods for the 124 (defrost or main air flap) and take the front diaphragm out to fix the center vent pod, but those are pretty spendy to part out ($40-$50 each).