Plenty for sale on amazon,i think it is more that it gives you a false sense of security as they are not medical grade but joe public thinks they are,covid can get through anything but the proper ones,they are not fitted and people fiddle with them so touching their faces many more times than they usually would,on and off for food and drink,the hospital staff don't do that, then there is washing and drying them properly,also for me it is then in some people's minds that the hand washing and keeping your distance is not so necessary
On balance i think masks for not needed,now boris has said it will help with confidence,that is why the advice has been changed imo