I spoke to one of Eventide's founders, Richard Factor, about the spectrum analyzer and asked whether he might know where we could find a copy of the "INTERACTIVE" program.  He said:

I’ll keep my eyes open but that’s about all I can do.  We may have one somewhere, but at best I’ll come across it accidentally.  And after all these years it may no longer play.

The first Eventide RTSA was for the Commodore PET computer.  I think it was the first product ever designed to go inside a general purpose computer.  Tried once to donate it to some museum but they weren’t interested.  The Apple II version and the Radio Shack TRS80 versions came along later.

Eventide moved from the Manhattan to New Jersey in 1984, and from what I gather, some things got lost or misplaced during that move.  Otherwise, it might have been easier to find the casette tape you are referring to.

Would you mind sharing a photo of the Spectrum Analyzer by the way?  I've never seen one, and I'm curious about it…