Have you given them a light in hen house to simulate longer day length?
I'd do that, Along with food and water. There are negatives to doing this; it's a stress on them, so you always want to give them a couple months off to moult, got to give them good quality food and it's said that they're don't lay for so many years. Maybe depends on size of their house as well, as they'll move about more with a light on and poo more too. Also it's better if lights on a dimmer so they have a chance to roost, or have it come on few hours before dawn, but that'll make your cockerel noisy. But you'll be more likely to get eggs sooner. Or just be patient, most pullets don't start laying till nearer six months or more, I've had May hatches come into lay November or December and go right through, maybe this will happen to yours?