I grew up in the sixties and was into counter culture as much as I could be living in rural England but I'd never heard of Avant Garde magazine. By all accounts it wasn't widely known in the wider world, but those in the know, knew.
Apparently, "Avant Garde is a seminal, but somewhat overlooked by a wider public, magazine, which broke taboos, rattled some nerves and made a few enemies. The magazine was the brainchild of Ralph Ginzburg, an eager and zealous publisher, even if the path that led to Avant Garde wasn’t so straightforward. It represents the third major collaboration between Ralph Ginzburg and Herb Lubalin, the magazine’s talented art director. The two previous magazines came to unexpected demise due to their candor and provocativeness, that landed them into legal trouble."
Anyway all of the issues are now available online, here. Enjoy.