Man we are talking about real money man. SC and D2 cd-keys are easy to find on internet.
Steam cd-key is rare even if stuff is legal because ppl prefer DL them from steam and in that case no cd-key is used. Buy a cd in shop if you want a cd-key.
Or buy them on steam, 10$ for half life, thats cheap man. 19$ for Half-Life Anthology (4 games) Thats 5$ for a game...
Steam is the only thing where I have payed for soft in my life, and the service is great
http://storefront.steampowered.com/v2/inde...wse&l=&s=&i=&a=