I didn't find anything ready made. I am scared it would cost more than 50$.
Looking at the measurables given in the video above, I think one could buy a Sony or Fuji T adapter (15$) then unscrew the T ring (6 mm), cut away almost all the tube and keep just the flange (7-8mm), glue the flange to the T ring. The piece should be short enough to go directly on the scope eyepiece holder which is free to rotate, so non need to have a rotating T ring.
The resulting adapter would be long as a standard Canon T adapter but the sensor is only 16-18 mm deep instead of 44 as in Canon Eos. That's a few mm more than the 1 inch required to achieve prime focus according to the very clear video fron Nige.
Wondering if someone tried. And if someone sells fuji mount flanges, just the flange.