January 1971 (Vol. 2, #1 issue of Earth (with Zoell cover and poster) has a 3 page Mr. Natural story by Crumb. This thing must be pretty rare as Fiene couldn't find one and only got the info. second hand and didn't even know the date.
By the way, there's one on eBay now for $9.99 Buy It Now with some loose pages (don't know if the poster is attached or included). Probably worth picking up? Let's see how long it lasts after this post...