Copy the file from another system or a trusted1 person's machine
If you have a second machine with a comparable build of OS X installed on it, you can copy the file from it. Make sure that you haven't made changes to the file that you're copying if you want a fresh copy. This is especially important for copying files from someone else's machine as the changes may not be desirable.
Feel free to ask for the checksum of a file in chat (don't forget to give an OS X version) to compare it to if you wish to make sure that the file has not been modified accidentally (or purposefully).
1 It's probably not best to trust random strangers on the internet for crucial system files.