i recently had a LBS pull a headset off my fork & they screwed up the threading on the steer tube (really badly). they ended up having to grind it down a little in order to be able to thread the headset back on. so now my headset barely threads on with no spacers.
so i'm thinking of asking a frame builder to replacing the steer tube on my fork. i normally wouldn't really care so much, except for the fact that this is a very rare 3rensho frame worth a lot of money.
You can melt some brass into the damaged threads and re-cut them. Brass threads aren't quite as strong as steel threads, but they're better than no threads and cheaper than a new fork.