I have seen a number of Comlinks the claim to have the correct found part on the bottom, but none of the bottoms look like the "long snoot" or Luke photo attached.
I did purchase a screw cap, but the photos appear to show a lip on the top of the bottom part, A white styrene washer should do the trick. I am still looking into one other piece that might be a close match.
Also, I read an interview where Roger Christian said he had to make the prop fast because it was need on set asap. If this is true, I suspect none of it was painted. Maybe it was another model kit part.