Well, I just answered my own question, sort of. I had a doctor's appointment near Sportsman's so I went in and asked. The guy said, "We don't sell them HERE," which I took to mean that some of their other Arizona locations might, but I think he's wrong. As far as why, he said because they are (cue scary music) "OTHER." By which I assume he meant AOW. Which they are not -- BATFE classifies them as "firearms." When I asked why they would sell them in other states, he just kept saying they are "OTHER," and thus they didn't even want to mess with them. He compared them to the AR pistols they had displayed behind him (which I presume are available for purchase), and made some comment about people taking off the stocks and throwing them away, which of course made no sense.