The Fly-RFPMEX can be purchased from AliExpress https://s.click.aliexpress.com/e/_DC9SrjL
This link is affiliated URL. If you purchase via link above it will give tiny cent of commission to the community organizers. (We are not Mellow employees, just 3D printer enthusiasts) This will not hurt your wallet and at the same time help us to maintain the GitHub better.
Klipper information can be found here https://mellow.klipper.cn/#/board/fly_rpfmex/ and here https://mellow-3d.github.io/fly-rpfmex.html
For Klipper support please join this Discord Channel https://discord.gg/zAung88zbK