out of curiosity, why do you specifically want it on tap? i've heard that they use different phoney sweeteners for their on-tap formulations because the sweeteners they use in their canned formulations aren't stable enough to hold up in an on-tap environment.
Most of The Habit locations have it. Tragically, the one on Ventura near Van Nuys does not. Also on a smaller scale the bagel place (New York Bagel Cafe I think) in the shopping center on Van Nuys and Ventura Blvd in Sherman Oaks has it too.
I'd also love to know which places have Coke Zero on tap. To my family, Coke Zero is way better than Diet Coke. Like the original poster, we have seen it at Corner Bakery, but that's about it, any other places?