In France you can order some at "official vegan shop", the name is shitty but they have some hard to find items. https://www.officialveganshop.com/gluten-de-ble-bio-celnat-500g-8922.html
Otherwise, organic stores usually have it in the flour section
You cannot if you don't have the diploma, even if you do your own goods. And that diploma requires to use animal products. As far as I know there isn't much way around that