IKEA does too. You can request smaller part you're missing on their website[1]. And if they don't have them available online you can check in with their support, once they shipped one part from two countries away, free of charge (and even thrown an extra one). For bigger parts they sometimes have them in stock at local stores.
I was very pleasantly surprised when they sent me free replacement hardware to reassemble an old ikea twin bed model that had been discontinued a number of years ago. I assume they use the same hardware in other models they still sell.
[1]https://www.ikea.com/us/en/customer-service/spare-parts/