Flat files drawers made thanks to u/total_novice (ikea komplement) : r/ikeahacks
Safco Products 4995BLR Flat File Closed Base for 5-Drawer 4994BLR Flat File, Sold Separately, Black : Amazon.com.au: Home
Safco Products 4997BLR Flat File Closed Base for 5-Drawer 4996BLR and 10 Drawer 4986BL Flat Files, Sold Separately, Black : Amazon.com.au: Stationery & Office Products