Did such a thing exist? I wouldn't have thought there was a need for it.
Whilst all DC3s or Dakotas did not have inbuilt airstairs the distance from the door sill to the ground was not that great. When I was involved with the Dakota in the 50s and 60s we did not have escape slides.
As I understand it under US Federal Aviation Administration rules:- " Each passenger-carrying landplane emergency exit (other than over-the-wing) that is more than 6 feet from the ground with the airplane on the ground and the landing gear extended, must have an approved means to assist the occupants in descending to the ground."
The DC3 door Sill is less than 6ft.