I don't doubt it's readily available if you're buying it from the right place, but it's not exactly a common format, so it's not reasonable to expect it to be in stock everywhere. Not all retailers carry sheet film in any format, much less that one. Heck, it's pretty difficult to walk into a retailer and find 24 exposure 35mm film. That typically is only available online from places like BH, Adorama, and Freestyle. Film is expensive enough that most retailers only carry what they can reasonably expect to move in a quarter.