Eva•tone Soundsheets were fun. They were more generically called flexi-discs. I have a few, and I’ll get around to transferring and posting them. There’s precious little information available about these earliest of floppy discs, even from Eva•tone; which is still in business, but ceased soundsheet production in 2000.
Here’s a flexi-disc from the early 1970’s with an interview of Batman comic-book writer Denny O’Neil. A much more recent interview with O’Neil is on the Batman Begins DVD.