WB owns all rights to the Salkind Superman films now.

The footage certainly exists, some of it was used for the extended cut of STM and the Donner cut of SII. And the deleted scenes on the Donner cut DVD seem to indicate that WB has, at the very least, a widescreen 35mm IP of the TV cut of SII - the scenes have the soundtrack from the TV cut. (At least some of these TV cuts were assembled in widescreen and then pan-and-scanned later; the deleted scenes on the Blazing Saddles DVD are also widescreen, but have the mono TV-cut soundtrack with the profanity edited out.)

On the other hand, the deleted scenes for SIII come from the pan-and-scan TV broadcast master, so who knows if they still have those?