As I no longer live in Japan I am unable to advise of upcomming events. However, I have compiled a list of annual or regular events here.
Tokyo Veg Festa
Usually held in October, this is Tokyo's top vegan event of the year, and should not be missed. Bring an empty stomach and a bag to stock up on groceries. Despite the name, all food and groceries are vegan. There are usually around 100 stalls selling foods, eco-products or just promoting worthy causes.
|Tokyo Vegfood Festa (more on my blog post here)|