I've been searching for a replacement as well but haven't broken it yet I kinda want to upgrade my SSD but also a bit paranoid about the screen so I went searching for one I found one place that sells a replacement but it isn't cheap you may as well buy a new one for that price...
[http://www.aliexpress.com/item/New-LCD-Touch-Screen-LCD-Panel-Assembly-For-Microsoft-Surface-Pro-3/32228587154.html|Surafe Pro 3 LCD-Pannel- Digitizer Assmebly]-$500.00
can't find anything off eBay yet...