You can get masks at all of those little sole trader hardware stores round my way - 3 grades, the pathetic surgical masks £1, then a more industrial looking thing £3 and a proper dust mask (for labourers) £4. All single use, but the last one ok for up to 8 hours. I got 3 of the latter for the family when the inevitable diktat happens, one for each member of the family, will be worn, in a mocking postmodern fashion, in shops only and reused. Purely for social acceptance.
You can guarantee that there is no new evidence for the change of policy, and none will be published. There is no need for anyone who is healthy to wear a mask, it won’t protect you. If you are ill it could reduce the chances of you infecting someone else, but you shouldn’t be out anyway if you are ill should you? If you are carrying the virus but not ill there is no evidence that you can infect anyone else if you are not coughing, especially if you are properly socially distanced.
I’m finding it quite funny seeing people wandering around outside wearing masks, or fiddling with them constantly, or wearing them over the mouth but not the nose, or removing them to talk or take a drink, all increasing their risk of infection. Personal favourite two people wearing masks- while driving in their car. Mask wearers also just about universally the worst at social distancing in my experience, false security I guess.