Are you sure the steerer needs to be that large? I have a hard time believe Soma wouldn't include forks that would fit up to a 60cm frame, 60cm isn't that large.

Soma sells a 1" threaded chrome fork with a maximum steerer tube length of 230mm. As repechage mentioned, the difference in threading is close enough as I would guess that the Soma fork has english threading.

https://www.somafabshop.com/shop/som...5773#attr=2766