Can you please tell me a bit more about your scenario?
Those files are embedded resources in the Sitefinity assemblies and you will not find them on the file system.
There is a way to get access to all templates / user controls used in Sitefinity.
You need to download Sitefinity SDK
and you will find them under
Content / Resources / Widget Templates / Templates
This blog post
describes how to override any of those if needed.
But again - if you provide more details about your scenario there might be an easier way to get there.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items