The short answer is that you cant. They eat insects, seeds, etc and you couldnt be sure that they were eating proper quantities of each important vitamin or mineral since they will just eat the most of whatever their favorite is, like a kid with cake. These birds arent wild and havent been for thousands of years. The best you could do would be an organic, gmo free balanced feed but that gets expensive quickly.
This paper explains the science of feeding quail and what nutrients, vitamins, and minerals they require