Well, lets get the obvious places out of the way. Hot Topic, Spencer's gifts, F.Y.E. and places like that tend to be common places to find stuff, although not necessarily stuff like plushies. As far as websites go, you could search all the regular sites, ebay, amazon and whatnot, but mainly there's WeLoveFine.com for pony merch online. There's also one called Redbubble, but I've seen varying reviews of them, and it seems pretty hit and miss with their products.