I can get wheat berries at my local health food store. Sprouts has them.
But you can also get them at feed stores, beer brewing places and online.
https://rainydayfoods.com/products/grain-and-cereal/grains.html
these guys are a little expensive, but they put them in buckets for you.

If you are going to make bread flour, be sure to get an electric mill.
I really like the mockmill
https://pleasanthillgrain.com/mockmill-grain-mill-flour-grinder-stone

A hand mill doesn't really make bread flour, but it is really good for muffins and cookies. The best it can do is a coarser grind.