.
From East Germany, in 1991, two videos. Both are 35-40 minutes and are well-filmed.
The first is banjo-picker and Elliott's singing buddy,
Derroll Adams, when they performed and recorded together in the mid-late '50s in England and Europe.
After Adams' first song, there's a bit of footage of he and Jack walking on the fairgrounds. The festival is huge with over 200 venues, apparently. At about 26:22, Adams calls out Elliott from backstage and they sing two duets together:
https://www.youtube.com/watch?v=6_3My23MouI
The 2nd video is Jack's performance at the venue:
https://www.youtube.com/watch?v=3lDPuWon09w