Some other food ideas could include noodle dishes where the sauce is completely separated
Zarusoba (ざるそば） buckwheat noodles with dashi/soy dipping sauce
Hiyashichuuka (冷やし中華）which is like chilled ramen without the soup, but instead with dipping sauce. They have this in many ramen stores especially in summer.
Tempura may also be limited in salt (usually that comes with dipping sauce or a mound of dipping salt)
Shabu shabu [a pot of boiling water and you cook vegetables and sliced raw meat] may also be ok if you request for the starting broth /soup to be just water.
And my japanese is not great, but perhaps you could show the waiter something like this
which means “As my husband as allergy to salt, is it ok to use less sodium/salt?”
[anyone please feel free to correct my japanese]