Sweet and Sara Vegan Marshmallow products are the best I’ve tried so far, but my campus only has one store that sells a few things from them – they would also be in a few health food stores around my area that I haven’t checked yet.
You can buy them online: http://sweetandsara.com/ Their peanut butter smores are fantastic
I’ve never had dandies, but from what I’ve seen and heard they are less stiff and more puffy than Sweet and Sara’s. http://www.chicagoveganfoods.com/dandies_vegan_marshmallows/
There are a few vegan online stores that keep them (like vivagranolaveganstore). They’re the kind you’d want to get for melting and roasting.