I heard that Swift is open-source, and I think all the frameworks are open-source. However, I cannot find the source code of CoreLocation on https://github.com/apple. I can see the source code for Foundation: https://github.com/apple/swift-corelibs-foundation, but I can't find CoreLocation. Is it available?
You will be able to get the source for any of the standard swift library: http://swiftdoc.org
You also have access to the source code for the swift compiler.
TL;DR; No - you cannot get source code for CoreLocation