Here we have a listing for the hard to find fine pitch serrated A2 Stainless flange nuts.
They are M10 x 1.25 pitch. 15mm A/F (socket size).
Please use some anti seize lubricant to ensure they do not seize up in the future.
I have had these made. They are very good quality. Various uses on your bike (sprockets etc)
Thanks for looking!