If you specifically need version 6 for legacy software compatibility, you must use third-party archives, as Apple does not host it.
: You can find original installation media for QuickTime 6 for Windows. 4. Installation Tips & Warnings Download Quicktime 6 For Windows 7
: Installing QuickTime 7 will actually disable legacy Pro functionality from version 6. 2. Official Download for Windows 7 If you specifically need version 6 for legacy