There's actually one with a buy it now of $950 on eBay if you want to drive to Houston and pick it up.... Why would you necessarily be hot for one. have you ever played one? I played with a guy back in the 70's that I think bought it new, it was OK, but a positive bitch to move around due to weight.
This is best I can remember, but I'm sure CB will chime in with more technical details, but to the best of my recollection; this was part of a series of amps that CBS put out in the early 70's shortly after going from the "black-faced" amps to the silver. They took the first "silver-face" revision of the 100w quad 6L6 Dual Showman head (details on differences, CB?) and stuffed into some different cabs, there was a "Quadraverb" which was that amp circuit in a Super Reverb cab; the Super Six was the same deal, but with a taller Super Reverb cab with 6 rather than 4 10-inch speakers.
Due to weight, size and price it wasn't real popular and they didn't sell many units and I think it was discontinued after a couple of years so that's why you aren't going to find many available. There wasn't any real discernable difference between the 6 and 4 speaker versions other than cost, but back in the day the 50w Super Reverbs were WAY more popular even in silver-face.
If you really want that amp. it would probably be easier to find a 100w Dual Showman head and plug it into a 4x10 cab.