Like a Chestertonian Cowboy

It begins with a boy who was never a man and ends with a man who was never a boy.

Thus begins the absorbing English-language debut of Argentine-born writer Rodrigo Fresan. This brilliant, ambitious and hypnotically strange novel explores the creation of the Peter Pan legend, the nature of childhood, the nature of memory and of fiction, of growing old and growing up.
...
In an afterword, Fresan reports that he was first inspired to investigate the Barrie story when he saw a film snippet in a French documentary of G.K. Chesterton and Bernard Shaw dressed up as cowboys and playing in a garden with a little man who turned out to be James Matthew Barrie.

[Jean Westmoore, The Barrie Story is Granted a New Hook. The Buffalo News, 29 Oct 2006]

I thought this film was lost.  This article implies that there may be a portion of it available inside another film.  Does any reader know more details of this?