Finally, I found a good substitute for soy sauce. South River Miso offers a few soy-free miso products that resemble the taste of soy sauce. I just got the chickpea barley miso and its pretty tasty, surprisingly close to its soy based cousin. Turn it into a sauce with a bit of water, or just smear it on vegetables, sushi, etc. Definitely expensive (I paid $11 for my jar!) but I figure it will last awhile since the flavor is potent.