In context: Traditional cassette tape sales have been steadily growing over the past few years. Cassette shipments increased from 74,000 in 2015 to 126,000 in 2016; a 74 percent boost. Sales climbed again to 174,000 in 2017, and then to 219,000 in 2018. This resurgence is largely due to the success of cassette-based movie soundtracks, such as Guardians of the Galaxy's "Awesome Mix."
Unfortunately for the comparatively small (but growing) group of people that still buy these tapes for one reason or another, production has hit a bit of a snag. According to a report from Pitchfork, the National Audio Company -- one of the biggest tape makers in the United States -- has been unable to meet customer demand due to a lack of materials; "gamma ferric oxide," specifically.
The outlet says that the only factory that still refines this material (we don't know the name of the factory) has been "under renovation" for the better part of 2019. Without those materials, the National Audio Company has struggled to fill orders.
For end-users, the situation might not be too noticeable for now. Several popular online storefronts still seem to have a stockpile of cassette tapes -- blank and containing content -- available for purchase (though the numbers are dwindling and pricing varies).
However, for the National Audio Company, the dilemma is undoubtedly a frustrating one. Existing stock may not have dissipated just yet, but new orders from corporate partners are likely coming in as fast as ever; especially with the Stranger Things Season 3 soundtrack arriving on the format. Other cassette tape makers are probably not faring much better.
With all of that said, cassette collectors and the National Audio Company itself shouldn't be too worried. Gamma ferric oxide production should resume again in the next few months, which is when the previously-mentioned factory is expected to finish its renovations.