I remember them! The stones were being sold at the Songbird Ocarina booth, which unfortunately wasn't there this year. You can still find them on their website here:
- Kokori Emerald - https://www.songbirdocarina.com/products/kokiris-emerald
- Goron Ruby - https://www.songbirdocarina.com/products/gorons-ruby
- Zora Sapphire - https://www.songbirdocarina.com/products/zoras-sapphire