Although this still doesn't really answer your question, here is what I know...
I don't follow treasure hunts in general, only vipers, and the last time Hot Wheels released a viper T-hunt was the white one in 1996. On that package it says "Only 25,000 produced worldwide." 1996 was the last year that Hot Wheels printed production numbers on the package and by 1998 Hot Wheels didn't even release production numbers at all. Why? To increase case sales I assume. Collectors buying by the case like to be guaranteed at least one treasure hunt. Next, they created the Super Treasure Hunt to bring back the "fun" of chasing a rarer car. In my opinion then, there would be around 25,000 super treasure hunts made and many many more of the regular t-hunts (as you have seen on eBay).
Regardless of how many are made, I still have never found any hanging on the pegs in any stores near me. So I've had to use eBay. Bob, if you've had luck in the past seeing t-hunts on the pegs, you might get lucky again. If you haven't, the viper won't be any different, so you may have to use eBay as well.