Smaller colleges and universities usually have a steady flow of traffic between classes. Some schools have an open policy on allowing leafletting, while others do not. Even if someone eventually tells you that you are not permitted to hand out literature on campus, it will likely be after you've given out a great number of brochures. People who take part in walkathons in order to raise money for causes tend to be willing to accept literature. Animal-related events, such as humane society benefits or animal rights presentations, are also a good place to reach interested and committed individuals who may not have considered the implications of their own diet, or the idea of promoting veganism.
Many activists are nervous about leafletting.
In our experience, nervousness often fades once you've offered the brochure to a few people. Besides Why Vegan, Vegan Outreach can supply you with copies of our Vegan Starter Pack for people with questions. One person can make an enormous difference. Many people will pass the information on to others, causing a chain reaction. Few people have any interest in engaging a religious zealot bent on converting them.