The retreads I was interested in years and years ago were known as "Hi-Tec Retreads" and the company was in Nebraska or South Dakota... but I think Nebraska. Anyway, they used "Green Diamonds" in their rubber for extra winter time grip which is why I was so interested.
I did a search for them just now and found this article. It seems Hi-Tec became Treadwright and gave up on the Green Diamond technology which perhaps went this way: article
Not near as cheap as they once were: Prices
Sent from my "two hands on a keyboard"