Go to this site and enter your serial number and machine type to look up the part number:
http://support.lenovo.com/us/en/ibasepartslookup
Then do a Google search for the part number for the best price.
This may well be a manufacturing defect, follow it on this forum: https://forums.lenovo.com/t5/Yoga-Flex-Laptops-and/Yoga-2-Pro-Cracked-Screen-and-more/td-p/1404499
Here is a guide on how to do the repair: https://www.youtube.com/watch?v=1f2l8KcoK5w