Did you ever find a Cotton Club Encore Extended edition?
I have a copy of exactly what you are looking for.
It is quite a large file, I believe about 40 GB.
It is an ISO file meant to be burned to a BD-R 50 disc.
There is also artwork included for the case and disc
so it looks like an official release.
I could shrink it to an MKV file if you prefer.
Let me know if you are interested.

Greg

Scenes from the original cut re-inserted into the Encore cut.

Original opening credits with the dancing girls.
Frenchy tells Owney the Dutchman has arrived at the club.
The rooftop pideon coop scene.
Dixie meets Gloria Swanson.
The Sandman / Lila scene where she tells him she has a private life.
Dixie in the car with his brother after Vincent is shot.
Mr. Jewitt offering his help to Madame St. Clair and Bumpy.
The longer scene of Dixie and Vera in the white curtains.
Irving announcing the presence of Chaplin, Brice and Cagney at the club.

Movie is now about 144 minutes