Hi Tony. I relate to your trying to find "exactly" the right kind of pick. For many musicians the kind of equipment used can make the difference between being happy with the results or always feeling that "something's missing".
I can't help you with that particular thumbpick (although I remember them) but I can tell you that I've gotten used to "customizing" all my picks. That wonderful little machine, the battery powered "Dremel" tool, is worth it's weight in gold to me. I start with a "Golden Gate " thumbpick (much superior to the others in my opinion), and start sanding it down so that the "pick" part is very thin but still sturdy enough to last through 3 months of gigs. You might want to try and customize your own.
One other suggestion that's proved useful in the past is to contact VERY rural music stores (takes a little Yellow Pages work), you'd be surprised what kind of things they bought in 1970 and still haven't sold. Good luck.