I'm pretty sure that Antonia (my sister, well one of them) and I had these posters when we were kids - I remember colouring them in when we visited my grandparents, the designs seem like the ones I remember, and the name rings a very loud bell. Only problem is, the information on the webpage says they're designed by a "former Creative Director of Jim Henson's Creature Shop" who's been "sending out Wildergorn posters to customers all over the world" since 2009. I mean, I guess they could have only started shipping worldwide in 2009. Or I could be misremembering, and they're just similar to the colouring in designs I remember from the '70s (but they look very similar...).
Whatever. They're very beautiful. If I had the money, I'd think about buying one or two of them...