I first met Steve Haffner at the Jack Williamson Lectureship, several years back. Steve's photo report of the most recent Lectureship can be found here. Jack Williamson was one of the greats of science fiction who came to New Mexico via covered wagon, sold his first short story in the 1920's, and continued to sell stories and novels in every subsequent decade until his death in 2006. He was made a Grand Master by the Science Fiction Writers of America in the 1970's. This honor is typically given to someone in their twilight years, but Jack lived for three decades after receiving his, and continued to produce top quality work. I had the honor of meeting this man several times before he left us. He was a kind, down to earth soul who opened his own house to us in Portales (and thanks to that I know what Hugos, Nebulas, World Fantasy Awards, Grand Master Awards and many other top trophies look like. I soon concluded that there were no knick knacks in this house, for upon closer inspection, they all had little engraved name plaques on them.)
Steve Haffner runs Haffner Press, a little publisher that has aquired the rights to publish vintage science fiction, fantasy, and horror greats. This is the place to shop for hard to find classics. Haffner Press also does the most comprehensive collections that I'm aware of. Check out their Williamson compilations, for example.
The only place to buy works published by Haffner Press, is on their site. I am not able to stock them in my store.