IKEA BESTA Shelf Support Pins Plugs Fixings Brackets X 4 GENUINE SPARES 113301 | eBay
IKEA Billy bookcase tip: if you have an OLD Billy bookcase (pre-2014) you can still add extra shelves even though the new extra shelves from IKEA use a new, disc-shaped shelf pin.
Buy ReplacementScrews White Shelf Support Pins Compatible with IKEA Part 101558 (Pax, KOMPLEMENT) (Pack of 4) Online at Lowest Price in Ubuy Italy. B091P2X6YP
Spare Hardware Parts Billy Shelf Pins (Compatible with IKEA Part #131372) (Pack of 12) : Amazon.co.uk: DIY & Tools