Kipon makes lots of GFX to ? adapters and they are 50% to 100% better made and designed. I got the Fotodiox GFX- Pentax 645 PRO adapter and it's good and I really like the Arca Swiss plate on the bottom of the adapter, but also heard bad things on their adapters so while waiting for my GFX I ordered a Kipon GFX-Pentax 645 adapter and wow it's nice and it's also made in China but so much better made.
Also when attaching the Pentax 645 lenses on to it the Fotodiox springs are not as tight as the Kipon so I am using the Pentax 80-160 zoom and that's some glass hanging and I trust the Kipon adapter to hold the lens tight to the flange better than the Fotodiox Pro, but I am only using the Arca-Swiss plate and would keep the Kipon if it had that plate....
Adorama is the USA seller.
Christopher