It must of been a very old post on the message board, Amazon offered the set at one time and unfortunately it's no longer available (I'm sure you already know this) I did a exhaustive search and turned up nothing other than referral links to Amazon.. Having not read or listened to Ben's audio set, I'd be very interested in obtaining the set myself so I can evaluate it... I know that his success rate was quite high.
I believe the last time it was sold on Amazon was 2001, so if it hasn't been available in the last 11 years, it's going to be almost impossible purchasing from a retailer... Ben would also be 96 years old today, hopefully he's still around.. Your best bet is private party or "out of print" I checked some of the most popular "out of print" book sites and to no avail.... My suggestion is to just keep looking, one will eventually turn up.
If anyone out there has the set or tried Ben's technique, please let us know by posting here or send me a PM.