82mm Hoya x400 filter
I have been looking for the same myself. Indeed Hoya does make the x400 in 82mm, but in very limited production. The only reputable vendor I'm aware of is Digital Camera Gear (Australian):
Cost is incredibly high due to the short supply however, that's if you can even manage to secure one from them before it's sold out (again). I think I will hold off until Hoya ramps up production and hopefully lower cost.