My local WHSmith's sell them in store as I purchased two from there yesterday. Although it can vary, sometimes they don't have any in. Depends on location as where I am a new Toys'R'Us opened up at the end of last year in town who also sells them. Argos sell them but I think its some sort of random pack deal depending on what stock they have, you get 3 packs and a promo card which you can reserve and then collect in store.
Given how so many places have shut down in recent years there's not a massive amount of places to buy them from directly. If Woolworths was still here I'd imagine they would be one of the places selling them in store as well.