It was never really a mail order catalog in the sense that there was no single place to order the stuff (the Whole Earth store did open later, but it just a slice of what appeared in the WEC and CoEvolution Quarterly). It was, as others have noted, reviews of "good stuff" and info on how (maybe) to get it.
That came later, when they opened the store. It only applied to stuff they decided to carry, though given that they reviewed it in print that was likely because the reviews were almost all positive.