If you want the full version and license for commercial use,
you can purchase here :

https://staircaselab.com/product/christina-callista/

Version: 

1. Christina Callista.otf
2. Christina Callista.ttf
3. Christina Callista.woff
4. Christina Callista Italic.otf
5. Christina Callista Italic.ttf
6. Christina Callista Italic.woff