Federal SPP's have been a little tough to find for several years... they are much favored by a lot of competitive shooters because their easy ignition means that they can use lighter hammer/striker springs and still pop them reliably. It is common for competitive revolver shooters, or even some DA/SA semi-auto guys, to have guns that will only run 100% when fed federal-primered ammo.
Those tend to be high-volume shooters. With no real substitute goods available, they will quickly buy up the SPP's when they show up.