Hello Sophia You can also say : " we don't have any of these items right now. I'm sorry. There is always different way to say the same thing...

You can just say, 'I am sorry but we have run out of stock for the item you want. We will put in another order and get back to you as soon as possible'.

If you are talking about merchandise for sale, you can say that "it's a special order item". That means the item is not normally carried in stock, but that you can have it ordered for the customer.