Call your local Siemens distributor (e.g., Rexel, Radwell, or directly Siemens Industry US/DE). Ask for a "Legacy media reprint."
If you must keep WinCC 6.2 alive:
You may see forums or torrent sites offering an "WinCC 6.2 Download ISO." This is incredibly dangerous. Here is why you should never use pirated industrial software: Wincc 6.2 Download