I use the Yelp.com phone app, it's great. One trick about most vegan places, sadly, is that they tend to use a lot of oil. But with the phone app, you can call them and ask whenever the mood strikes!
But also, if you go to a top-notch restaurant, they will always have good plant-based options and will have good chefs who will be willing to prepare low-oil foods too. You didn't mention if you're traveling on an expense account? 
I'm also fond of just buying some groceries and eating them in my hotel room (or the local beach, whatever), if I'm not going to be dining with colleagues or clients when traveling.