Yes they do. Shop will often give magazines / photographers / models pre release clothes for the next season in order to drum up interest for their fashion lines. There would be no point showing old, or out of date clothes in a magazines fashion shoot.
No, there in shops in 2 to 3 weeks. And MAYBE, just maybe you can buy them online.
Hope I helped! :)
Many of the outfits they show are one of a kind or are only available in high end boutiques and have very high price tags. Unless you are talking about catalogs then the clothes are available to all.