If your looking for a good All Grain mix to use as a scratch you can use a All Grain Pigeon Mix.
They come with or with out corn, has a good mix of grains, and also comes in a number of protein percentages ranging from 11% protein up to 21% protein.
Just remember that scratch is energy source and is not meant to be fed as a feed.
One of the reasons that chicken go for the grain before the crumble is instinct, another is that chickens eat to fill a caloric need, scratch is a quick way for them to fill that caloric need.