Basically JIS headsets are not that special.
Just a regular size with a 27.0 mm crown race.
Don't know if these headsets are offered in this specification regularly, nost retail head sets have a 26.4mm crown race.
But 27.0mm crown races can be ordered individually.
In case your front fork bearing seat has a diam of 27.0mm, you can also consider to (have it) machine(d) at 26.4mm.
Basically JIS headsets are not that special.
Just a regular size with a 27.0 mm crown race.
Don't know if these headsets are offered in this specification regularly, nost retail head sets have a 26.4mm crown race.
But 27.0mm crown races can be ordered individually.
In case your front fork bearing seat has a diam of 27.0mm, you can also consider to (have it) machine(d) at 26.4mm.