I think the stocker is made by Mikuni
and Kehins are the diamond shaped ones.
There are several brands that "should" work.
I bought a nice Kehin copy (female) & Pingel plate.
They were both 22mmX1.0 (s/a harley), but the thread flank
angle was different.
Since Pingel makes the plates, you have to comply with that.
I finally would up with a Pingel valve, & like it a lot.

Said Molly to James, that's a fine motorbike. Richard Thompson