You have two options
1) As it's brand new - get it replaced under warranty
2) If that is not an option, try ebay, or amazon.
Personally, I would suggest contacting microsoft for a repair or visiting a care outlet if there are any around you. Usually the lumia help+tips app is the best place start however I'm not sure what the current state of your screen is soo that may not help.
https://www.microsoft.com/en-gb/mobile/support/product/lumia735/warrantyandrepair/
Example:
amazon.co.uk/Nokia-Digitizer-Complete-Original-Replacement-Black/dp/B00WA87NW8