Steam – Buying someone a Steam game without a Steam account

I agree with corroded that you should just give them the key, but to answer your question:

If you purchase a copy of a game you already own, you may or may not receive a giftable copy to give to someone else. According to Valve, the only cases where you get a giftable copy are:

1. Users who own Left 4 Dead and then go on to purchase "Left 4 Dead + Left 4 Dead 2 Bundle" will receive an extra copy of "Left 4 Dead"

2. Users who own Half-Life 2 and go on to purchase “The Orange Box” or the "Valve Complete Pack" will receive an extra copy of “Half-Life 2”.

3. Users who own Half-Life 2: Episode One and then go on to purchase the "Half-Life 2: Episode Pack”, “Valve Complete Pack” or “The Orange Box” will receive an extra copy of “Half-Life 2: Episode One”.

4. Users who own Dawn of War II and then go on to purchase "Dawn of War II Gold Edition" will receive an extra copy of "Dawn of War II"

5. Users who purchase the available four packs for specific Steam titles will receive three extra copies of that title to gift to friends.

6. Extra copies may apply as a part of some limited time promotions. In that case, information on what will be included with your purchase will be listed on the storefront's transaction page.

When trying to activating a Game you already own (or a bundle you already own parts of), Steam will warn you in a popup which game/parts won't be added to your library. You then have the choice to cancel the activation.

No, there's no way to get the Steam key for a game you've redeemed on Steam without using Steam.

In fact, I'm not aware of a way to do this if you have Steam running - once the key is redeemed, Steam doesn't typically give you any way to view it.

The exception is games that have keys beyond the Steam system. These games you can view the "CD Key" or similar in the Steam library view for the game. However, there is no way to get this information without being logged into Steam.

I would suggest contacting Steam customer support in your case.