I will be going to France in a couple of days and just been told about the Crit’air environment badge. Can I purchase this when in France? And where?
According to https://www.rac.co.uk/drive/news/motoring-news/law-change-for-uk-drivers-in-french-cities/ you are out of luck as delivery can take a while.
However the official website mentions an express option that might be fast enough for you. https://www.crit-air.fr/en/information-about-the-critair-vignette/additional-information/questions-about-ordering.html#c18180
Not having the sticker will restrict your ability to drive in a number of cities.
It is not possible to buy one once in France.