The download page for CMake only shows a 32-bit installer for Windows. How can I install it on 64-bit Windows systems?
There really isn't any reason for a 64-bit native CMake. CMake is only building the configuration, so you can use it to build configurations for 64-bit software, even with the 32-bit version.
That being said, if you truly want a 64-bit native version, you could always download the source and compile it. There isn't any 64-bit installer, however.