It depends on how you define vegan. Most semi sweet chocolate chips are dairy free but contained refined sugar, which is a gray area because of the way the sugar is processed. I would say 99% of vegans eat refined sugar, but there are those few that don't.
Ghirardelli makes an excellent dairy free chocolate chip that I'm sure you could find in bulk.
Trader Joes makes a dairy free chocolate chip that's Belgian I believe. It might be tricky to find in bulk, but the retail price is quite competitive. In fact, I'd wager to say that TJs chips, bought in single packages are cheaper than what you're paying now. And, of superior quality. At least, from my experience they are. I've baked with the Tropical Source chips a bit and although they're pretty good, both Ghirardelli and Trader Joes are superior. To me, Tropical Source is less about the quality of the chocolate and more about wacky ingredients and saavy marketing.