You can buy them direct on their site:
Barnakl
Or from Amazon (beware of the counterfeits)
Amazon
Predictably, there are now dozens of copycats from China selling pads of microfiber and telling you to stick it to the top of your fan. Even more maddening, because a lot of people haven't heard of Barnakl, they're buying paid ads on Amazon so their products show up over the inventors.
My suggestion is that you can tell them where to stick it.
The original are made of carbon from coconut shells AND they're made in the USA so not only are they the OG, they're better for the environment.
