New Faces Of 1937 (1937)
New Faces Of 1937 was intended to be a regular showcase series, but this film was not successful and has only recently been issued on DVD. You can sometimes find NTSC VHS video copies of it; also it was released on Laserdisc (both VHS and Laserdisc are analog recording media; not many of us have the players for either these days).
The Brian Sisters appear briefly in the title song New Faces. Their original filming was very much longer, but sadly was not included in the released film and is now gone forever.
In the film's plot it was planned to produce a flop and take the investors' money – in reality it actually was aflop!
I wonder who took the money…
Here is an image of the girls from it instead of a clip.
In the film, the girls climb/crawl out of boxes on the stage, group together as in the picture, and sing a couple of lines:
"And now for closeups of our cast,
All New Faces with a future a-and a past."
– but that's really all there is. A couple of lines!
The distinctive Brian Sisters sound is there, though, even with such a small appearance. You would know who they were even without looking!
There is now (released on Feb 6th 2015) a MOD (Manufactured on Demand) DVD available, which you will find from a few retailers. It's costly for a few seconds of The Girls, but must be worth it!