You don't need one ! Just download the latest ST9+ Toolchain from this web site and the debugger and C compiler will then be installed on your machine.
The thread is from 15-YEARS ago, the user names and email alerting almost certainly hasn't survived the multiple forum upgrades/changes since then. Someone may have a mirrored copy of that software, but unlikely to run on 64-bit Win7-10 systems currently.
You'd do better looking for the GNU ST9 tools, or contacting ST support more directly/locally.