I've been seeing these a good deal at GameStop. One store had at least 3 different helmets in stock a few days ago - the 332nd Clone Trooper, Bo-Katan and the Artillery Stormtrooper. I've seen the Darth Vader helmet more recently at Target. And Hasbro seems to be responding to demand because they're offering the Red 5 helmet again, too. The Captain Rex helmet is really tough to resist. With as many clones as Dee Bradley Baker portrayed, Captain Rex was such a well developed character. And seeing Rex portrayed in live action was amazing.
But I agree with Nick - the space these require to be displayed properly is a serious challenge! Does anyone know if these would fit in an IKEA Detolf? I've seen images of the helmets resting on top of them. And I also have to wonder if Hasbro will get around to offering some kind of a helmet display pedestal at some point. It might make for a nicer way to show these off rather than sitting on a shelf.