This "wedge type" grad ND is available only in large sizes, I have one for my Fujica GSW690 from Formatt, a HiTech 77 mm ND0.6 Blender (with 67 to 77 step-up ring).
They have a super soft transition over the whole diameter, nice for rangefinder cameras because you dont have to care about correct placement of the transition zone. "Blender" or "wedge type" grad NDs are used in the movie industry, for still imaging they are hard to find, as mentioned.
My custom made wedge filter is made from a Singh-Ray Galen Rowell 2 f-stop soft grad ND Filter ND-2G-SS (gathered dust) and a cheapo 52 mm Tama U-Slim Digital UV Filter. I asked my optician to cut out a 52 mm disk from the transition zone of the Singh Ray (transition from bright to dark was about 5 cm), and change the UV glass into the ND disk. Cost me the UV filter plus 5 Euro for the optician.
This filter sits on my CV15/4.5II 80% of the time, very useful IMO.
screwed in