On Warcraft 2, I don't think there's any way to buy it now. You may just have to download it somewhere. I see no reason why pirating it would be wrong.
It's debatable whether pirating such old games that are essentially vaporware and generate no revenue for the devs/publisher, but if you can't legitimately buy a game anymore then I personally see no harm in pirating it because it won't hurt anyone.
Same goes with The Elder Scrolls Adventures: Redguard.