Where do I get those recipes or do I have to buy them in the shop?
Take quests from Reijin, You will get them over a course of 3 quests
They should be available as side quests in Reijin. If there are no quests available, try returning to Deucalis and then going back to Reijin (if you finished the storyline).
So ALL recipes are obtainable in quests/weekly missions?
Some are also obtained by random hunter battles, but basically, yes.