They should have a stock of spare parts in the store, but you can definitely order them online from the Ikea website or from Amazon.
They will send some if you call the 800 number.
Most of the time it's easier fins spare parts online from Amazon. But if you just bought something and the pieces weren't on the box. I would go to your store or call (make sure you have your receipt if possible) and they shoukd be able to help you
Usually suppliers can get you missing parts if you contact them directly. I would look up the name of the unit you are talking about and then contact the store directly.
Thanks! Your answer is awaiting moderation.