If retailers have more stores then they would just up their order with Hasbro but retailers dont always carry the same items in every store as not every store will be suitable or entitled to carry the product. So perhaps some of the not finding product is that not every store will even be getting everything it in to start with.
Certainly in the UK we are seeing more retailers carry ponies than ever used to in the past...Forbidden Planet being a case in point...they would never have permitted a pony past their doors in the past and so far I have seen both brushables and blind bags in there.
As mentioned the whole thing is normal - its what we saw with G3 so I would doubt between them, Hasbro and the will continue the torment of pony collectors the world over