You can get Qt source code here: 

http://registrationcenter-download.intel.com/akdlm/irc_nas/13488/qt-src-5.12.0-windows.zip
http://registrationcenter-download.intel.com/akdlm/irc_nas/13488/qt-src-5.12.0-linux.tgz
http://registrationcenter-download.intel.com/akdlm/irc_nas/13488/qt-src-5.12.0-macosx.zip
