Previously unseen footage of ABBA rehearsing Msmma Mia for their Bandstand appearance was broadcast in April 2004 as part of Channel 9's coverage of ABBA's 30th Anniversary and the fifth anniversary of the stage show "Mamma Mia!".

The footage was apparently originally rough snippets but has been edited together so the piece flows smoothly.

Bandstand Rehearsals (Mamma Mia), 1976;
Bandstand (Mamma Mia), 1976;
Dancing Queen (Bandstand), 1976;
The Best of ABBA (Bandstand Special) (Mamma Mia, Hasta Manana, Ring Ring, Tropical Loveland, Waterloo, I Do, I Do, I Do, I Do, I Do, Rock Me, (Lucky Starr), Honey, Honey, Fernando, So Long, SOS), 1976; 
ABBA in Australia (Mamma Mia, Hasta Manana, Ring Ring, Tropical Loveland, Waterloo, I Do, I Do, I Do, I Do, I Do, Rock Me, Dancing Queen, Honey Honey, Fernando, So Long, SOS, Bang-A-Boomerang), 1976;

Thanks to Ian Cole and Philip Muytjens. 
YouTube link c/o bill patterson