I just buy mixed corn which is wheat plus chopped (cracked) maize, but there are brands which also have extra seeds which is nice but more expensive. I give mine about a dessertspoonful each, in winter shortly before roosting time so they go to roost with something in their crops to keep them going through the 15 hours before breakfast. I add the same amount of pellets and anything else which has gone into the ‘chicken box’ on the worktop during the day, such as apple cores, leftover grapes, etc. Then I mix it up with a little warm water to make the pellets just crumbly. They have it on a big plate so it doesn’t get dirty on the run floor. They also get their daily cabbage greens then as well.
But it’s fine just to give them a sprinkle of corn in the afternoon before bedtime, once they’ve eaten their pellets for the day. If you just hold it on your hand they will come to you and become very tame. Don’t give very much, though, it’s fattening, and they need the balanced nourishment in their pellets to go on laying eggs with strong shells.