What do you feed your Cornish Cross/Broilers??

I'm new to the meat chicken game and decided to get 35 broilers this year when I ordered my hens.
I've done my research but am having a hard time finding a feed that is both non medicated and non gmo.
Eventually I hope to make my own feed but I'm wondering what Y'all feed your meat birds?
Currently I have a 20% would really like something organic or non gm to feed them since we are going to eat them.
They will get pasture as they are older.
Do you keep them on the 20 or switch to 18 as they mature?

Thanks!