I found an adjustable Super Slide today at Goodwill. It has two bumpers that screw down and hold the slide in place, adjustable to any length. All the parts were there, including the booties.
I probably paid too much - $20 - but I haven't seen one in years there and I lost my last one when our basement flooded. Not sure where I'm going to put it, but I couldn't leave it there.
Oh, even the brochure is there, advertising such home fitness goodies as Fabio's Power Abs Board (which looks suspiciously like the original Firm transfirmer when it came in one piece with legs).