For a while now, it has been difficult to get flour reliably from the supermarkets. Yeast is also becoming hard to find.
For the flour, the problem is that more people are beginning to bake ( quite a good thing, really!) however, the vast majority of millers are unable to pack for retail. In short, there's enough flour out there but it's been hard to bring it to the shops in a packed form.
A couple of supermarkets have now come up with means to get flour and yeast to all us habitual bakers.