There's a bakery near us in Arlington that has regular sized and mini vegan cupcakes - Quebrada. There was a cupcake place in Needham (which is nearish to Westwood, I think?) that was doing vegan cupcakes, but I'm not sure if they still are/if they're even still open, I'll try and look it up, and report back.
eta: found it! http://www.treatcupcakebar.com/gluten-free/