My "white whale video" was the promotional video that Jim Henson made to try (unsuccessfully) to get the Muppet Show on CBS.
I got to see it in college for my Muppet Magic class, but after that I couldn't find it to show to anyone else for years (even though it's a fun bit of history), because it was never officially released anywhere.
Thankfully though
it's now it's on YouTube [You must be logged in to view images. Log in or Register.] So nothing to hunt for here unfortunately.