My only advice is to hit all the Ikeas you can reach and scour the loose shelves and tabletops in the As-Is section. I found a few Billy corner shelves in a few local Ikea As-Is sections that I added to my tall corner unit. I took any and all colors I could find. If you get really desperate you could try to find a used corner unit and cannibalize the shelves from it. A few years later I sold the whole thing to someone for more than I paid for it because it had been discontinued for so long and although the corner units themselves are pretty difficult to find used, it's nigh impossible to find just the extra corner shelves themselves due to the unusual hexagonal shape being virtually unuseable for any other shelving unit. Good luck and happy hunting!