Almost all of the mentioned retailers DON'T sell these filters, they are almost impossible to buy anywhere. I had to check out multiple other countries, and even there most shops didn't have them, or didn't ship internationally. There is also a lot of unclarity if a package contains one or two filters.
It is also unclear how to install them - Blueair's instruction video seems incorrect (on top the filter is shown installed with the dust side as the first air contact, but on bottom with carbon side first, which makes more sense).
