Thanks Hotshot, always appreciate your input on these sort of issues. I pretty much figured it is a long shot. I don't have a way of knowing dimensions of the green duckbill valve as it isn't listed online, and I don't have a shop on my island where I can go hold one in my hand. Of course getting an ebay plunger/oiler assembly is also a krapshoot, but they cost more than the $3.50 invested in the green valve. I found the various duckbills in aquarium air hoses used as an anti-reflux valve is way too big. To me, the Roper one is pretty tiny. So I suppose the green one is really on the micro scale.
I checked at the only home brew store here in the state, and got the proverbial deer in the headlights stare when inquiring of kegerator beer charger fittings. I do homebrew, made my own Keezers, etc but at this point don't keg but bottle. My oldest son kegs his brews but wasn't familiar with what you have mentioned.
I'll keep digging around, though slowly I suppose til I come up with something I can get to work. I have used penrose drains to fabricate temporary heimlich valves, as well as a rubber glove with a finger tip cut off, and have even considered trying to find some very very thin (as in balloon thin) rubber tubing that I can fashion as a one-way valve for the oiler, but just haven't made progress on this. I don't expect anything will fall into my lap, but I'm keeping my eyes open.