I just repaired two bits of Ikea furniture by buying parts from SwedishFurnitureParts.com. [update 3-2017, it’s now furnitureparts.com] That was a much better solution than spending 2 hours going to an Ikea and fishing through their spare parts box. Thanks internet!
Here’s most of the Ikea manuals, in case you are looking for part numbers. http://www.ikea.com/ms/en_US/customer_service/assembly_instructions.html