It depends if you mean ponies or merchandise
popyduggan has linked to the thread where most people will post if they have found out about any new ponies and toys [regular toys, plush, vinyl, etc] and we really do together as a community keep it as up to date as pretty much any source on MLP. But merch is tougher because it is all licensed so it truly can be anywhere and anything. Also most of the time MLP is licensed to companies who are producing lots of the same item with different licences on each one so often they do not promote their products as MLP specifically.