I was also looking for this old Mac game today, and stumbled across this thread.
I managed to get it copied off an old Mac disk, and I've got it working on the Mini vMac emulator.
I've put up a web page about the game, and a download of the emulator and disk image containing System 6 and the Risk game at: http://www.richardloxley.com/fun/risk/
Let me know if this is what you were looking for!
Richard, my many thanks. This is a dream come true. Well done.
Best Regards,
John