I have been working on a replacement DUO-R card door also. Here is a rough draft that I printed on an extrusion based 3D printer that I have access to. It is in no way indicative of the quality of the finished part; I only use it to prove out the geometry.
(https://jelloslug.com/TG-16/DUO-R%20door%20rough%20draft.JPG)
With all the folks who are asking about this, you'd think someone would have replied by now!
Or, do most folks need it for a a DUO?
Either way, excellent progress.
Also, I owe you money if the items are still available. I apologize for failing.