What would you use in flower?
That all depends on how far in flower you are and how serious the infestation is. They can easily ruin the plant if they are out of hand. From my experience, you wont kill them all, especially in flower. You can control it doing what
@Green_Alchemist wrote like removing lover fans which are obviously doomed, off the top fans you can remove adult thrips manually, you can wrap your stems with that thin yellow sticky tape to cut their path to the buds… Lady bugs are not effective and they piss on your plants also. you will most likely have some of them in your buds, but still better than smoking neem or other chemicals. Sometimes they just came in your medium sometimes it is your dirty environment. Better to solve the issue for every cost before the flowering starts. I see here people using citric acid as “pesticide” so maybe it can also work on thrips not affecting buds so much since it is not oil based, but this is just an idea, have not tried so not reccomending. Good luck!