If coconut is safe, there is coconut aminos. Otherwise, I've had good success using umeboshi vinegar. It doesn't have the same depth of flavor (or color - it's purple which can be an odd color in some things), but give that salty "bite" to things. Another options is balsamic vinegar plus salt. That's a little sweeter though. If you can do fish, nuc mam (Vietnamese fish sauce) is another option.