KX Drawer Racks (Storage units with 2, 5 or 10 drawers) - fit IKEA Kallax cubes | eBay
Ikea Kallax Shelf Insert With 5 Cardboard Drawers in a Set - Etsy UK
Upgraded with drawers and knobs several years ago and finally got around to adding the legs on the Kallax! The legs weren't as long as I'd wanted, but I was just ready